Synonyms for Caption:

n.

fill in, address, enter, enshrine, complete, annotate, fill out, date, backdate. a play on words, innuendo, witticism, wisecrack, pun, joke, wordplay, punch line, one-liner. jottings, chit, minute, message, memo, inscription, note, memorandum, iou. caption (noun)
legend, subtitle.
heading (noun)
heading.
heading; short description (noun)
inscription, subtitle, title, legend.
inscription (noun)
heading, title.
title (noun)
subtitle.

Other synonyms:

memo, date, jottings, annotate, inscription, iou, chit, enshrine, title, memorandum, fill out. enter, fill in, backdate. complete. message. address. minute. note. headline
heading.
Other relevant words:
chit, iou, jottings, title, message, enter, backdate, inscription, heading, annotate, minute, address, note.