Definition of lubber's line in English:
lubber's line
noun
(also lubber line)
A line marked on the compass in a ship or aircraft, showing the direction straight ahead.
‘Adjustable compasses have a compass body with a lubber's line and a rotating capsule or bezel with a boxing mark.’- ‘Simple compasses may use north or 0º on the azimuth circle as a lubber's line.’
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