An instrument formerly used for making angular measurements, especially in astronomy and navigation, analogous to a sextant but having a notional arc of 72 degrees rather than 60 degrees, and so measuring up to 72 degrees (or 144 if the instrument has a mirror). Compare "octant", "quadrant".
In practice makers often made quintants with a scale greater than 72 degrees.
Late 17th century (in an earlier sense). From classical Latin quīntus fifth + -ant, after quadrant and sextant.