topic / subject of conversation

to be a subject of discussion

to touch / to experience, come in contact with / to press (a button) / to mention lightly

all, entirety, the whole, everything

wholly, entirely, completely, at all

all, entirety, the whole, everything

wholly, entirely, completely, at all

one division, one step, one part of something / one moment, one time / (theater, performing arts) one act, one scene

once

one slice or cut of something / (rare) a one-time sexual liaison, a one-night stand