The Collaborative International Dictionary of English v.0.48:

Needs \Needs\, adv. [Orig. gen. of need, used as an adverb. Cf.
   -wards.]
   Of necessity; necessarily; indispensably; -- often with must,
   and equivalent to of need.
   [1913 Webster]

         A man must needs love mauger his head.   --Chaucer.
   [1913 Webster]

         And he must needs go through Samaria.    --John iv. 4.
   [1913 Webster]

         He would needs know the cause of his repulse. --Sir J.
                                                  Davies.
   [1913 Webster]

WordNet (r) 3.0 (2006):

needs
    adv 1: in such a manner as could not be otherwise; "it is
           necessarily so"; "we must needs by objective" [syn:
           inevitably, necessarily, of necessity, needs]