nucleobase

https://doi.org/10.1351/goldbook.09710

Purine or pyrimidine nitrogenous base occurring in deoxyribonucleic acid (DNA) or ribonucleic acid (RNA).

Example: Purine and pyrimidine bases of ribo- and deoxyribonucleotides.

Purine bases

Pyrimidine bases

Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T) b)
Uracil (U) a)
a) Uracil is normally found in RNA but not in DNA.    b) Thymine is usually found in DNA but not in RNA.
Source:
PAC, 2018, 90, 1121. 'Terminology of bioanalytical methods (IUPAC Recommendations 2018)' on page 1148 (https://doi.org/10.1515/pac-2016-1120)