thirty, a. [OE. thritty, AS. þrītig, þrittig; akin to D. dertig, G. dreissig, Icel. þrjātīu, þrjātigi, þrir teger, Goth. þreis tigjus, i.e., three tens. See Three, and Ten, and cf. Thirteen.].

Being three times ten; consisting of one more than twenty-nine; twenty and ten; as, the month of June consists of thirty days. [1913 Webster]

thirty, n.

The sum of three tens, or twenty and ten; thirty units or objects. [1913 Webster]
A symbol expressing thirty, as 30, or XXX. [1913 Webster]

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OXFORD DICTIONARY

thirty, n. & adj.
--n. (pl. -ies)
1 the product of three and ten.
2 a symbol for this (30, xxx, XXX).
3 (in pl.) the numbers from
30 to 39, esp. the years of a century or of a person's life.
--adj. that amount to thirty.

Idiom

thirty-first, -second , etc. the ordinal numbers between thirtieth and fortieth. Thirty-nine Articles the points of doctrine assented to by those taking orders in the Church of England. thirty-one, -two , etc. the cardinal numbers between thirty and forty. thirty-second note esp. US Mus. = DEMISEMIQUAVER. thirty-two-mo a book with 32 leaves to the printing-sheet.

Derivative

thirtieth adj. & n. thirtyfold adj. & adv.

Etymology

OE thritig (as THREE, -TY(2))

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