(idiomatic) To attempt to prevent a problem that has already occurred.

A reflection after an act; a later or subsequent thought, action, or expedient. / Something additional to the original plan or concept.

(very rare except in the past tense, possibly nonstandard) To expound as an afterthought.

simple past tense and past participle of afterthink

(temporal location) At a later or succeeding time.

The part of the day from noon or lunchtime until sunset, evening, or suppertime or 6pm. / (figuratively) The later part of anything, often with implications of decline.

(more often in the plural) In the afternoon.

Ellipsis of good afternoon..

(nautical) Nearest the stern of a vessel. / (obsolete) Most recent.

(obsolete) At the very back.