noun, plural: nucleosides
(1) A nitrogenous base (purine or pyrimidine) bound to a pentose sugar ribose or deoxyribose.
(2) A glycoside formed from the hydrolysis of nucleic acid.
A phosphate group attached to a nucleoside would make a nucleotide.
Depending on the pentose sugar component, a nucleoside may be a ribonucleoside (e.g. adenosine, guanosine, cytidine, and uridine) or a deoxyribonucleoside (e.g. deoxyadenosine, deoxyguanosine, deoxycytidine, deoxythymidine).
Word origin: nucleic- from nucleus + -ose + -ide.
Related terms: nucleoside analogue, nucleoside diphosphate.
See also: nucleic acid.