The Collaborative International Dictionary of English v.0.48:

Ripost \Ri*post"\, Riposte \Ri*poste"\, n. [F. riposte.]
   1. In fencing, a return thrust after a parry.
      [1913 Webster]

   2. A quick and sharp refort; a repartee. --J. Morley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

riposte
    n 1: a quick reply to a question or remark (especially a witty
         or critical one); "it brought a sharp rejoinder from the
         teacher" [syn: rejoinder, retort, return, riposte,
         replication, comeback, counter]
    2: (fencing) a counterattack made immediately after successfully
       parrying the opponents lunge
    v 1: make a return thrust; "his opponent riposted"
    2: answer back [syn: retort, come back, repay, return,
       riposte, rejoin]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "riposte":
   acknowledge, acknowledgment, advocate, allege in support, answer,
   answer back, answering, antiphon, aphorism, apothegm, argue for,
   argument, assert, back answer, back talk, backchat, bon mot,
   boutade, bright idea, bright thought, brilliant idea, champion,
   come back, come back at, comeback, conceit, contend for, counter,
   counterstatement, crack, defend, defense, demurrer, denial, echo,
   epigram, espouse, evasive reply, exception, facetiae, flash back,
   flash of wit, flight of wit, gibe, give acknowledgment,
   give answer, happy thought, maintain, make a plea, mot,
   nasty crack, objection, persiflage, play of wit, plea, plead for,
   pleading, pleasantry, quip, quips and cranks, react, reaction,
   ready reply, rebut, rebuttal, receipt, reecho, refutation, refute,
   rejoin, rejoinder, repartee, replication, reply, repost, rescript,
   rescription, respond, respondence, response, responsion,
   responsory, retort, return, return answer, return for answer,
   reverberate, reverberation, sally, say, say in defense,
   say in reply, scintillation, shoot back, short answer, smart crack,
   smart saying, snap back, snappy comeback, speak for, speak up for,
   special demurrer, special pleading, stand up for,
   statement of defense, stick up for, stroke of wit, support,
   sustain, take the bait, talk back, turn of thought, uphold,
   urge reasons for, wisecrack, witticism, witty reply, witty retort,
   yes-and-no answer