Base Pair Definition

noun

A pair of bases consisting of the pyrimidine base of one nucleotide joined by a hydrogen bond to the complementary purine base of another nucleotide: such pairs form the links between the two strands of DNA and of double-stranded RNA.

Webster's New World

A pair of nitrogenous bases, consisting of a purine linked by hydrogen bonds to a pyrimidine, that connects the complementary strands of DNA or of hybrid molecules joining DNA and RNA. The base pairs are adenine-thymine and guanine-cytosine in DNA, and adenine-uracil and guanine-cytosine in RNA.

American Heritage Medicine

(biology) In molecular biology, two nucleotides on opposite complementary DNA or RNA strands that are connected via hydrogen bonds.

Wiktionary