Synonyms for Preexistent:

• adj.

  •early (adjective)
  • ere long,
  • ahead of time,
  • on short notice,
  • in advance,
  • directly,
  • promptly,
  • soonest,
  • on the dot,
  • far ahead,
  • quick,
  • too soon,
  • pronto,
  • previous,
  • Oversoon,
  • early bird,
  • bright and early,
  • in the bud,
  • a bit previous,
  • with time to spare,
  • in time,
  • shortly,
  • ANON,
  • unexpectedly,
  • beforehand,
  • soon,
  • immediately,
  • briefly,
  • before long,
  • presently,
  • prematurely,
  • in good time,
  • Proximately,
  • betimes.
  •preceding (adjective)
  • introductory,
  • ahead of,
  • precursory,
  • prefatory,
  • Pioneering,
  • supra,
  • forward,
  • precedent,
  • past,
  • other,
  • front,
  • above-mentioned,
  • prodromal,
  • lead,
  • preliminary,
  • above-named,
  • leading,
  • prevenient,
  • erstwhile,
  • Precursive,
  • head,
  • before,
  • aforementioned,
  • heretofore,
  • pioneer,
  • aforesaid,
  • forerunning,
  • preparatory,
  • aforeknown,
  • one time.
  •prior (adjective)
  • ahead.

• adv.

  •early (adverb)
  • be forehand,
  • ahead time,
  • on dot,
  • pre-maturely,
  • un-expectedly,
  • un expectedly,
  • over soon,
  • be-forehand,
  • over-soon,
  • bright early.

• adv

  •early (adverb)
  • in bud.

• Other synonyms:

  •antecedent
  • antecedent.
  •Other relevant words:
  • older,
  • first,
  • elder,
  • senior,
  • foregoing,
  • fore,
  • anticipatory,
  • former,
  • prime,
  • earlier,
  • anterior.

Antonyms for Preexistent:

• adj.

  • early
    later, late.
  • preceding
    after, back, below, last, unimportant, inferior, following.
  • prior
    future, present, current, subsequent.