c. 1400, frowntere, "front line of an army;" early 15c., fronture, "borderland, part of a country which faces another," from Old French frontiere "boundary-line of a country," also "frontier fortress; front rank of an army" (13c.), noun use of adjective frontier "facing, neighboring," from front "brow" (see front (n.)). In reference to North America, "part of the country which is at the edge of its settled regions" from 1670s. Later it was given a specific sense:
What is the frontier? ... In the census reports it is treated as the margin of that settlement which has a density of two or more to the square mile. [F.J. Turner, "The Frontier in American History," 1920]
"the prostate gland," 1640s, from French prostate, from Medieval Latin prostata "the prostate," from Greek prostatēs (adēn) "prostate (gland)," from prostatēs "leader, ruler, guardian; one standing in front," from proistanai "set before," from pro "before" (from PIE root *per- (1) "forward," hence "in front of, before") + histanai "cause to stand," from PIE root *sta- "to stand, make or be firm." So called from its position at the base of the bladder and immediately in front of its mouth. Related: Prostatic.
"the last but two," 1730, from antepenult (n.), 1610s, abbreviation of Latin antepænultima (syllaba) "last syllable but two in a word," from fem. of antepænultimus, from ante "before" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before") + pænultima, from pæne "almost" (a word of uncertain origin) + ultima "last" (see ultimate).