olemus
klahv, mis koos teise klahviga vajutamisel muudab selle toimet

Wiktionary:
(computing) a key (on a computer keyboard) that may be pressed simultaneously with certain other keys to activate predefined functions
Ctrl, Alt, and Shift are the modifier keys on a typical modern keyboard.

näiteid
https://duckduckgo.com/?q=modifier+key&t=h_&iax=images&ia=images

ülevaateid
https://en.wikipedia.org/wiki/Modifier_key