frontyoudaoicibaDictYouDict[front 词源字典]
front: [13] As its close French relative front still does, front used to mean ‘forehead’. Both come from Latin frōns, a word of dubious origins whose primary meaning was ‘forehead’, but which already in the classical period was extending figuratively to the ‘most forwardly prominent part’ of anything. In present-day English, only distant memories remain of the original sense, in such contexts as ‘put up a brave front’ (a now virtually dead metaphor in which the forehead, and hence the countenance in general, once stood for the ‘demeanour’).

The related frontier [14], borrowed from Old French frontiere, originally meant ‘front part’; its modern sense is a secondary development.
=> frontier[front etymology, front origin, 英语词源]
front (n.)youdaoicibaDictYouDict
late 13c., "forehead," from Old French front "forehead, brow" (12c.), from Latin frontem (nominative frons) "forehead, brow, front; countenance, expression (especially as an indicator of truthfulness or shame); facade of a building, forepart; external appearance; vanguard, front rank," a word of "no plausible etymology" (de Vaan). Perhaps literally "that which projects," from PIE *bhront-, from root *bhren- "to project, stand out" (see brink). Or from PIE *ser- (4), "base of prepositions and preverbs with the basic meaning 'above, over, up, upper'" [Watkins, not in Pokorny].

Sense "foremost part of anything" emerged in the English word mid-14c.; sense of "the face as expressive of temper or character" is from late 14c. (hence frontless "shameless," c. 1600). 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. Meaning "organized body of political forces" is from 1926. Sense of "public facade" is from 1891; that of "something serving as a cover for illegal activities" is from 1905. Adverbial phrase in front is from 1610s. Meteorological sense first recorded 1921.
front (v.)youdaoicibaDictYouDict
1520s, "have the face toward," from Middle French fronter, from Old French front (see front (n.)). Meaning "meet face-to-face" is from 1580s. Meaning "serve as a public facade for" is from 1932. Related: Fronted; fronting.
front (adj.)youdaoicibaDictYouDict
"relating to the front," 1610s, from front (n.). Front yard first attested 1767; front door is from 1807. The newspaper front page is attested from 1892; as an adjective in reference to sensational news, 1907.