The Collaborative International Dictionary of English v.0.48:

Manful \Man"ful\, a.
   Showing manliness, or manly spirit; hence, brave, courageous,
   resolute, noble. " Manful hardiness." --Chaucer. --
   Man"ful*ly, adv. -- Man"ful*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

manfulness
    n 1: the trait of being manly; having the characteristics of an
         adult male [syn: manfulness, manliness, virility]