IPA: /ˈɒnˌsteɪdʒ/
KK: /ˈɑnˌsteɪdʒ/
Located or happening in the part of a stage that the audience can see.
The actor felt nervous while performing onstage in front of a large crowd.
In or into the part of a stage that the audience can see.
The actor performed beautifully onstage during the play.
Onstage → It is formed from "on" (meaning in a position of) and "stage" (from Old French *estage*, meaning a platform or stage for performances). The word "onstage" refers to being in a position on the performance platform.
Think of being 'in a position of' ('on') a 'platform for performances' ('stage') — that's what it means to be onstage.