n. & adj.
n. (pl. -ies) 1 the product of two and ten. 2 a symbol for this (20, xx, XX). 3 (in pl.) the numbers from 20 to 29, esp. the years of a century or of a person's life. 4 colloq. a large indefinite number (have told you twenty times).
adj. that amount to twenty. twenty-first, -second , etc. the ordinal numbers between twentieth and thirtieth. twenty-one, -two , etc. the cardinal numbers between twenty and thirty. twenty-twenty (or 20/20) 1 denoting vision of normal acuity. 2 colloq. denoting clear perception or hindsight. twentieth adj. & n. twentyfold adj. & adv.
[ OE twentig (perh. as TWO, -TY(2)) ]