late 13c., "forehead," from Old French front "forehead, brow" (12c.), from Latin frontem (nominative frons) "forehead, brow, front; facade, forepart; appearance," perhaps literally "that which projects," from PIE *bhront-, from root *bhren- "to project, stand out." Or from PIE *ser-, "base of prepositions and preverbs with the basic meaning 'above, over, up, upper'" [Watkins].
Sense of "foremost part of anything" developed in Latin. The military sense of "foremost part of an army" (mid-14c.) led to the meaning "field of operations in contact with the enemy" (1660s). Home front is from 1919. Sense of "public facade" is from 1891; that of "something serving as a cover for illegal activities" is from 1905. Meteorological sense first recorded 1921. Front yard first attested 1767.