isotopologue

https://doi.org/10.1351/goldbook.I03351
A molecular entity that differs only in isotopic composition (number of isotopic substitutions), e.g. CH4, CH3D, CH2D2.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1132 [Terms] [Paper]