Meaning

noun following the third position; number four in a countable series

noun one of four equal parts

noun the musical interval between one note and another four notes away from it

originInherited from Middle English fourthe, an alteration (due to four) of ferthe, from Old English fēorþa, fēowerþa, from Proto-West Germanic *feurþō, from Proto-Germanic *fedurþô, equivalent to four + -th (ordinal suffix). Cognates Compare West Frisian fjirde, Saterland Frisian fjädde, fjoode, Dutch vierde, German Low German feerde, feerd, German vierte, Danish fjerde, Icelandic fjórði.

Etymology from Wiktionary, CC BY-SA 3.0