The Collaborative International Dictionary of English v.0.48:

Necessarily \Nec"es*sa*ri*ly\, adv.
   In a necessary manner; by necessity; unavoidably;
   indispensably.
   [1913 Webster]

WordNet (r) 3.0 (2006):

necessarily
    adv 1: in an essential manner; "such expenses are necessarily
           incurred" [syn: necessarily, needfully] [ant:
           unnecessarily]
    2: in such a manner as could not be otherwise; "it is
       necessarily so"; "we must needs by objective" [syn:
       inevitably, necessarily, of necessity, needs]
    3: as a highly likely consequence; "we are necessarily bound for
       federalism in Europe"

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "necessarily":
   accordingly, and so, as a consequence, as a result, certainly,
   come what may, compulsorily, consequently, fatefully, finally,
   from necessity, inconsequence, indefeasibly, ineluctably,
   inescapably, inevasibly, inevitably, inexorably, inflexibly,
   irrevocably, it follows that, naturally, naturellement, need,
   needfully, needs, nolens volens, of course, of necessity, perforce,
   relentlessly, requisitely, surely, therefore, unavoidably,
   uncontrollably, unpreventably, unyieldingly, willy-nilly,
   without choice