From Middle English -th, -t, from Old English -þ, -t, -þu, -tu, -þo, -to (“-th”, abstract nominal suffix), from Proto-Germanic *-iþō, from Proto-Indo-European *-iteh₂. Cognate with Scots -th, West Frisian -te, Dutch -te, Danish -de, Swedish -d, Icelandic -ð, -d, Gothic -𐌹𐌸𐌰 (-iþa), Latin -itās (“-ty, -ity”). See -ity, -t.
- (no longer productive) Used to form nouns from verbs of action.
- (no longer productive) Used to form nouns from adjectives.
- Used to form the ordinal numeral when the final term of the spelled number is not “first”, “second”, or “third”.
- (mathematics) Used to form a term denoting the ordinal numeral corresponding to the value, being a natural number, of a mathematical expression.
- The nth term of a geometrical progression whose first term is a and common ratio is r is given by arn.
- When suffixing a spelled number ending on "eight", its final "t" is dropped: eighth; twenty-eighth.
- In older texts, this suffix, and the other suffixes for forming ordinals, may be seen written as superscripts: 1st, 2nd, 3rd, 4th, 5th. This is considered old-fashioned; the current preference is to write (when not spelling the numbers), 1st, 2nd, 3rd, 4th, 5th.
- When used to suffix a mathematical expression, a hyphen is sometimes inserted: n-th term.
- (archaic) A variant of -eth, used to form the archaic third-person singular indicative present tense of verbs.