1. underbar - Noun
2. underbar - Verb
underbar (plural underbars)
A bar placed under a symbol.
A
_
{\displaystyle {\underline {A}}}
is the letter A with an underbar.
underbar (third-person singular simple present underbars, present participle underbarring, simple past and past participle underbarred)
(transitive) To place a bar under (a symbol).