[1] : The Collaborative International Dictionary of English v.0.48

unbid \unbid"\ u^nbi^d", unbidden \unbid"den\, a.
   1. not bidden; not commanded.
      1913 webster

            thorns also and thistles it shall bring thee forth
            unbid; and thou shalt eat the herb of the field.
                                                  --milton.
      1913 webster

   2. uninvited; as, unbidden guests. --shak.
      1913 webster

   3. being without a prayer. obs. --spenser.
      1913 webster

[2] : WordNet (r) 2.0

unbidden
     adj : not invited or requested; "unbidden guests"; "comments unbid
           and unwelcome" syn: unasked, unbid
see also:
unasked unbid 

[3] : Moby Thesaurus II by Grady Ward, 1.0

43 moby thesaurus words for "unbidden":
   arbitrary, autonomous, discretional, discretionary, elective, free,
   free will, gratuitous, independent, nonmandatory, offered,
   optional, proffered, self-acting, self-active, self-determined,
   self-determining, spontaneous, unacceptable, unagreeable, unasked,
   unasked-for, unbesought, uncalled-for, uncoerced, uncompelled,
   undesirable, undesired, unforced, uninfluenced, uninvited,
   unpressured, unprompted, unrequested, unrequired, unsolicited,
   unsought, unwanted, unwelcome, unwished, voluntary, volunteer,
   willful

Unbidden >> U Words
Unbidden, definition of term: Unbidden
unbidden_pag1.html