Meaning

noun position seven in a countable series of things

noun one part in seven equal parts

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

originFrom Middle English seventhe, sefte, from Old English seofoþa, from Proto-West Germanic *sebundō, from Proto-Germanic *sebundô. The -n-, lost in northern Proto-West Germanic, was later reinserted by analogy with seven, equivalent to seven + -th.

Etymology from Wiktionary, CC BY-SA 3.0