The Collaborative International Dictionary of English v.0.48:
xx \xx\, adj. The Roman number representing twenty; denoting a quantity consisting of 20 items or units. Syn: twenty, 20, score. [WordNet 1.5]WordNet (r) 3.0 (2006):
xx adj 1: denoting a quantity consisting of 20 items or units [syn: twenty, 20, xx] n 1: the cardinal number that is the sum of nineteen and one [syn: twenty, 20, XX] 2: (genetics) normal complement of sex chromosomes in a female