What? What did you say?

what / that thing (used in place of words you can't remember at the moment.)

Nothing

safety / good health / peace

What?, Huh?

safe and sound / (as the adverbial 無事に) successful without any problem

(adverbial particle, dismissive, derogatory) emphasizes disgust, contempt, or otherwise negative feelings of the speaker: whatever

何: interrogative pronoun; what

何か: something

Used other than figuratively or idiomatically: see なに, これ.