I. noun
: one of the pairs of nucleotide bases on complementary strands of nucleic acid that consist of a purine on one strand joined to a pyrimidine on the other strand by hydrogen bonds holding together the two strands much like the rungs of a ladder and that include adenine linked to thymine in DNA or to uracil in RNA and guanine linked to cytosine in both DNA and RNA
II. intransitive verb
: to participate in formation of a base pair
adenine base pairs with thymine