1A flattened appendage on various parts of the body of many aquatic vertebrates and some invertebrates, including fish and cetaceans, used for propelling, steering, and balancing.

1. 1.1An underwater swimmer's flipper.
   ‘Training equipment such as kickboards, pull buoys, and fins help all swimmers to isolate or emphasize certain movements.’
   More example sentences

   • ‘The next steps involve the whole stroke, removing the fins, underwater kicking to stroke start and finally the block start.’
   • ‘You take a look around the pool and are surprised to see that a number of swimmers are using fins, especially on kick sets.’
   • ‘Allowing a swimmer to use a fin would send a message that his impairment is a disability and not just a characteristic of who he is as a person.’
   • ‘They offer everything from diving equipment and lessons, to snorkeling gear and swim fins for an enjoyable underwater experience merely feet from your room.’
   • ‘All swimmers would like to have fins instead of feet.’
   • ‘Using fins for drills and some kicking sometimes helps these swimmers.’
   • ‘You realize that swimming without fins has become unbearable.’
   • ‘You'll just need a pair of training fins (also known as flippers) to wear on your feet.’
   • ‘A drill to develop this body position involves swimming with fins and a snorkel.’
   • ‘Finally, wear fins on some of your swimming sets.’
   • ‘‘For sprint emphasis, we'll use short fins to simulate a more realistic natural kick,’ he says.’
   • ‘To maximize your feel for this drill when first trying it, try wearing fins, which will also allow you to better maintain your balance while trying the drill.’
   • ‘Now, the children are ready to try it on their own, using fins.’
   • ‘But when you wear fins, your kick improves enough to make kicking worth the effort and you end up using use your legs more.’
   • ‘It's important, too, to allow for flexibility within a workout, be it with fins, paddles or buoys.’
   • ‘Do this exercise with and without fins, with and without a kick board, on your back, side, and stomach.’
   • ‘We recommend that beginners and all children 8 and under use short fins to perform this stroke.’
   • ‘We wear fins and masks, and we also wear pink caps so we can be visualized by one another and not lose anyone.’
   • ‘I do a fair bit of technique work with fins and those sorts of things just to improve my stroke and I think it has come on a bit over the last year’
2. 1.2A small flattened projecting surface or attachment on an aircraft, rocket, or automobile, providing aerodynamic stability or serving as a design element.
   ‘The center fin was a fixed surface, extending vertically above the stabilizer at the center line of the airplane.’
   More example sentences

   • ‘Simply described, the fins improve directional stability by channeling and smoothing the airflow around the tailcone.’
   • ‘Aerodynamic fins located on the aft bay of the strap-ons also provided for flight control.’
   • ‘Years later when the definitive fin / rudder was retrofitted to this aircraft, these fairings remained unchanged.’
   • ‘The centrifugal force of the roll causes the fins to unfold for aerodynamic stability in flight.’
   • ‘The vessel is fitted with two pairs of active stabilising fins and twin rudders and has bow and stern thrusters.’
   • ‘There it is to undergo refurbishments, including repairs to a stabiliser fin damaged in transit.’
   • ‘A double-stepped bottom reduces the wetted surface area while above the water a fin at the rear stabilises the boat against cross-winds.’
   • ‘Attached to the end of the barrel are stationary fins that provide stability during flight.’
   • ‘The ship has two shafts with controllable pitch propellers, two rudders and a pair of active stabilising fins.’
   • ‘When the pilot applied the brakes, the plane went forward on to its nose and turned upside down, causing serious damage to the aircraft nose and fin.’
   • ‘The only obvious changes to the airframe are the new canopy and the taller fin extended back over the rudder.’
   • ‘It was at that time that another depth charge exploded close to the aft starboard fin.’
   • ‘Next, he explored a different aesthetic with less prominent fins, visible rocket thrusters, and less visible similarity to marine life.’
   • ‘Two downward sweeping stabilizing fins sat near the engines, adding to the triangular appearance of the ship.’
   • ‘The control surfaces and the four fins open into position as the missile leaves the tube.’
   • ‘He noticed that the gun fire had damaged what looked like a stabilization fin.’
   • ‘Typically, moveable flaps on fins serve as airfoils.’
   • ‘Six spring-loaded fins are attached to the rear of the rocket motor.’
   • ‘The fins and horizontal tail consoles are attached to tail beams.’
3. 1.3A flattened projection on a device, such as a radiator, used for increasing heat transfer.
   ‘The fins conduct heat from the tubes and then transfer it to the air flowing through the radiator.’
   More example sentences

   • ‘Concrete structural fins act as shading devices on the north-south axis.’
   • ‘The top and bottom of the Cool Drive have fins for heat dissipation.’
   • ‘While the fins help dissipate the heat, you may be wondering where the fan is.’
   • ‘Framing the rear of the station are the blue internal heat radiator fins.’
   • ‘They machined down the original fins of the power supply's heat sinks to create flat areas for attaching waterblocks.’
   • ‘The serrated fins actually increase the surface area to allow for more heat dissipation.’
   • ‘Looking closely at the fins you'll see that Hush's attention to detail is admirable, with each fin ridged for ultimate heat exchange.’
   • ‘Its central element is the single-frame radiator grille, the outer chrome ring of which surrounds the painted grey fins of the grille with horizontal chrome strips.’
   • ‘As you can see, they pack the copper fins pretty tight, allowing for pretty good heat dissipation, rated for 938.89 BTU per hour.’
   • ‘Sandia's Mike Rightley said he has developed tiny liquid-filled pipes that shift heat to the edge of the computer where air fins or a tiny fan can disperse it into the air.’
   • ‘The copper strip is folded into corrugated fins and cut with louvers, or turbulizers, to increase heat-dissipation capacity.’
   • ‘In a normal heatsink, all the fins most be located close to the heat source (the CPU) to maximise dissipation.’
   • ‘This is another idea that in theory should help increase thermal conduction between the base and the fins, since they are all one piece.’
   • ‘Because of copper's heat retaining properties, thin fins are the way to go, coupled with an adequate fan.’
   • ‘Actually, it's round and the idea behind it is that heat gets dissapated to the outer fins, where it gets cooled.’
   • ‘There are a total of six heat pipes running from the base to the aluminum fins.’
   • ‘On the building exterior, shading devices such as roof overhangs and fins or louvers above windows reduce glare.’
   • ‘It relies on radiation and passive convection from the heatsink fins that surround it, to dissipate heat.’
   • ‘It literally sandblasts the car every time it goes on track and gradually erodes all the surfaces and the cooling fins on the radiators.’

Swim underwater by means of flippers.