What? What did you say?

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

Nothing

today, this day / nowadays

What?, Huh?

Same as こんにち above

good day, good afternoon: a Japanese greeting used in the daytime

(archaic) (as for) today

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

何: interrogative pronoun; what