to let one's voice become quieter

love child / some undesirable product, child, or consequence; the aftermath

to fail to hear something; to miss

to beat down, to knock off

(idiomatic) to hold the key (to)

(colloquial) current boyfriend

(Internet slang) protected account (on social media, especially Twitter and Instagram)

to lock (a door, etc.) / (Internet slang) (of a SNS account) to change privacy setting to limited people and posts and/or profiles can be seen by limited people.

everything

black key (of a piano, etc.)