Reflection after an act; later or subsequent thought. [1913 Webster]
an action taken after another action and related to the first action, which would normally or optimally be done along with the first action; -- as, to do something as an afterthought. [PJC]
a feature or part added to a device, not thought of in its original design. [PJC]

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OXFORD DICTIONARY

afterthought, n. an item or thing that is thought of or added later.

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THESAURUS

afterthought

PS, Parthian shot, about-face, addendum, afterthoughts, appendix, back matter, better thoughts, bind, block, blockage, bureaucratic delay, change of mind, chorus, coda, codicil, colophon, conclusion, consequence, continuance, continuation, delay, delayage, delayed reaction, detention, developed thought, double take, dragging, dying words, envoi, epilogue, flip, flip-flop, follow-through, follow-up, halt, hang-up, hindrance, holdup, interim, jam, lag, lagging, last words, logjam, mature judgment, mature thought, moratorium, obstruction, paperasserie, parting shot, pause, peroration, postface, postfix, postlude, postscript, re-examination, reappraisal, reconsideration, red tape, red-tapeism, red-tapery, refrain, reprieve, respite, retardance, retardation, rethinking, revaluation, reversal, reverse, review, right-about, right-about-face, ripe idea, second thought, second thoughts, sequel, sequela, sequelae, sequelant, sequent, sequitur, slow-up, slowdown, slowness, stay, stay of execution, stop, stoppage, subscript, suffix, supplement, suspension, swan song, tag, tergiversating, tergiversation, tie-up, time lag, turnabout, turnaround, volte-face, wait

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ROGET THESAURUS

afterthought

Tergiversation

N tergiversation, change of mind, change of intention, change of purpose, afterthought, tergiversation, recantation, palinode, palinody, renunciation, abjuration, abjurement, defection, going over, apostasy, retraction, retractation, withdrawal, disavowal, revocation, revokement, reversal, repentance, redintegratio amoris, coquetry, vacillation, backsliding, volte-face, turn coat, turn tippet, rat, apostate, renegade, convert, pervert, proselyte, deserter, backslider, blackleg, crawfish, scab, mugwump, recidivist, time server, time pleaser, timist, Vicar of Bray, trimmer, ambidexter, weathercock, Janus, changeful, irresolute, ductile, slippery as an eel, trimming, ambidextrous, timeserving, coquetting, revocatory, reactionary, a change came o'er the spirit of my dream.

Sequel

N sequel, suffix, successor, tail, queue, train, wake, trail, rear, retinue, suite, appendix, postscript, epilogue, peroration, codicil, continuation, sequela, appendage, tail piece, heelpiece, tag, more last words, colophon, aftercome, aftergrowth, afterpart, afterpiece, aftercourse, afterthought, aftergame, arriere pensee, second thoughts, outgrowth.

Memory

N memory, remembrance, retention, retentiveness, tenacity, veteris vestigia flammae, tablets of the memory, readiness, reminiscence, recognition, recollection, rememoration, recurrence, flashback, retrospect, retrospection, afterthought, post script, PS, suggestion, prompting, hint, reminder, remembrancer, flapper, memorial, commemoration, note, memo, memorandum, things to be remembered, token of remembrance, memento, souvenir, keepsake, relic, memorabilia, art of memory, artificial memory, memoria technica, mnemonics, mnemotechnics, phrenotypics, Mnemosyne, prompt-book, crib sheet, cheat sheet, retentive memory, tenacious memory, photographic memory, green memory, trustworthy memory, capacious memory, faithful memory, correct memory, exact memory, ready memory, prompt memory, accurate recollection, perfect memory, total recall, celebrity, fame, renown, reputation, remembering, remembered, mindful, reminiscential, retained in the memory, pent up in one's memory, fresh, green, green in remembrance, unforgotten, present to the mind, within one's memory, indelible, uppermost in one's thoughts, memorable, by heart, by rote, without book, memoriter, in memory of, in memoriam, memoria in aeterna, suggestive, manet alta mente repostum, forsan et haec olim meminisse juvabit, absens haeres non erit, beatae memoriae, briefly thyself remember, mendacem memorem esse oportet, memory the warder of the brain, parsque est meminisse doloris, to live in hearts we leave behind is not to die, vox audita peril littera scripta manet, out of sight, out of mind.

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