The Collaborative International Dictionary of English v.0.48:

Insist \In*sist"\, v. i. [imp. & p. p. Insisted; p. pr. & vb.
   n. Insisting.] [F. insister, L. insistere to set foot upon,
   follow, persist; pref. in- in + sistere to stand, cause to
   stand. See Stand.]
   [1913 Webster]
   1. To stand or rest; to find support; -- with in, on, or
      upon. [R.] --Ray.
      [1913 Webster]

   2. To take a stand and refuse to give way; to hold to
      something firmly or determinedly; to be persistent,
      urgent, or pressing; to persist in demanding; -- followed
      by on, upon, or that; as, he insisted on these conditions;
      he insisted on going at once; he insists that he must have
      money.
      [1913 Webster]

            Insisting on the old prerogative.     --Shak.
      [1913 Webster]

            Without further insisting on the different tempers
            of Juvenal and Horace.                --Dryden.

   Syn: Insist, Persist.

   Usage: Insist implies some alleged right, as authority or
          claim. Persist may be from obstinacy alone, and either
          with or against rights. We insist as against others;
          we persist in what exclusively relates to ourselves;
          as, he persisted in that course; he insisted on his
          friend's adopting it. --C. J. Smith.
          [1913 Webster]

WordNet (r) 3.0 (2006):

insist
    v 1: be emphatic or resolute and refuse to budge; "I must
         insist!" [syn: insist, take a firm stand]
    2: beg persistently and urgently; "I importune you to help them"
       [syn: importune, insist]
    3: assert to be true; "The letter asserts a free society" [syn:
       insist, assert]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "insist":
   advocate, affirm, allege, announce, annunciate, argue, assert,
   assever, asseverate, aver, avouch, avow, blandish, brook no denial,
   cajole, call for, call on, call upon, coax, command, contend,
   declare, demand, dwell on, emphasize, enunciate, exhort,
   expostulate, express, force upon, have, high-pressure, hold,
   importune, insist on, insist upon, issue a manifesto, jawbone,
   lay down, lobby, maintain, manifesto, nag, persist, plead with,
   ply, ply upon, predicate, press, press upon, pressure, proclaim,
   profess, pronounce, protest, push, push upon, put, put it,
   recommend, remonstrate, require, say, set down, soft-soap, speak,
   speak out, speak up, stand for, stand on, state, stick to, stress,
   submit, sweet-talk, take no denial, thrust upon, urge, urge upon,
   vow, wheedle, work on