main key

Translations
основной ключ
главный ключ
мастер-ключ
основная тональность
Definitions
The primary or most important key used to access, operate, or control something.
A key that provides access to multiple locks, systems, or areas.
The principal key or tonality in which a musical composition is written.
Words
main

adjective
главный
key

noun
ключ