means A short, sharp-pointed nail or pin with a broad flat head, used to fasten things lightly or temporarily — or, by extension, a course of action or direction (as in 'a different tack').

from From Old North French 'taque' or related forms meaning a fastener or nail, akin to Middle Dutch 'tacke,' a sharp point or twig. The nautical sense — changing 'tack' to alter a ship's heading relative to the wind — comes from the same root, the 'tack' being the fastening or rope that held a sail's lower corner; from there it sailed into figurative use as any change of approach.