# What are compounds with the same mass called?

It may be that the answer is just "no" and that's why I can't find it, but is there any common name for compounds with the same mass?

I'm thinking in the context of mass spectrometry where these compounds require additional steps to resolve.

Isomers are the obvious example, but I was wondering if there was a more general term.

• By any stretch, you can't call $\ce{CO}$ and $\ce{N2}$ isomers, though they have about the same mass. – Ivan Neretin Apr 7 '16 at 11:09
• Isomers are not defined by their same mass but by their same chemical formula. So there is no reason at all to think about CO and N2 being isomers solely based on their "about same mass". – pH13 - Yet another Philipp Apr 7 '16 at 13:05