The Collaborative International Dictionary of English v.0.48:

Proffer \Prof"fer\, v. t. [imp. & p. p. Proffered; p. pr. &
   vb. n. Proffering.] [OE. profren, proferen, F. prof['e]rer,
   fr. L. proferre to bring forth or forward, to offer; pro
   forward + ferre to bring. See Bear to produce.]
   1. To offer for acceptance; to propose to give; to make a
      tender of; as, to proffer a gift; to proffer services; to
      proffer friendship. --Shak.
      [1913 Webster]

            I reck not what wrong that thou me profre.
                                                  --Chaucer.
      [1913 Webster]

   2. To essay or attempt of one's own accord; to undertake, or
      propose to undertake. [R.] --Milton.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "proffered":
   arbitrary, autonomous, discretional, discretionary, elective, free,
   free will, gratuitous, independent, nonmandatory, offered,
   optional, self-acting, self-active, self-determined,
   self-determining, spontaneous, unasked, unbesought, unbidden,
   uncalled-for, uncoerced, uncompelled, unforced, uninfluenced,
   uninvited, unpressured, unprompted, unrequested, unrequired,
   unsolicited, unsought, voluntary, volunteer, willful