A sailor dressed in 'square rig' - (now) with square collar - (formally) with tarred pigtail.
a British sailor
a common sailor. Also simply " Tar."
Naval An old civilian name for a sailor; probably derived from the black 'tarpaulin' hats worn between 1857 and 1891 (boater-shaped with cap-ribbon round the crown). Another theory explains the word JACK as a diminutive of Jacket (i.e. meaning a short jacket), the TAR referring to the old sailors' practice of waterproofing their clothes with tar.
Jack Tar was the common Englishman's affectionate name for the sailors of the Royal Navy during the time of the British Empire. There are three plausible etymologies for this name.