The Collaborative International Dictionary of English v.0.48:

Interject \In`ter*ject"\, v. t. [imp. & p. p. Interjected; p.
   pr. & vb. n. Interjecting.] [L. interjectus, p. p. of
   interjicere to interject; inter between + jac[e^]re to throw.
   See Jet a shooting forth.]
   To throw in between; to insert; to interpose. --Sir H.
   Wotton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Interject \In`ter*ject"\, v. i.
   To throw one's self between or among; to come between; to
   interpose. --Sir G. Buck.
   [1913 Webster]

WordNet (r) 3.0 (2006):

interject
    v 1: to insert between other elements; "She interjected clever
         remarks" [syn: interject, come in, interpose, put
         in, throw in, inject]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "interject":
   allude to, blurt, blurt out, call attention to, comment, drag in,
   ease in, edge in, exclaim, fill in, foist in, fudge in, implant in,
   infuse, inject, inject in, inoculate, insert, insert in, insinuate,
   insinuate in, intercalate, interjaculate, interpolate, interpose,
   intervene, introduce, introduce in, intromit, intrude, let drop,
   let fall, lug in, make reference to, mention, muse, note, observe,
   opine, perfuse, pop in, put between, put in, refer to, reflect,
   remark, run in, sandwich, set in, slip in, smuggle in, speak,
   squeeze in, stick in, throw in, thrust in, tuck in, wedge in,
   whip in, work in, worm in