From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From WordNet (r) 3.0 (2006) [wn]:
manfully
adv 1: in a manful manner; with qualities thought to befit a
man; "having said her say Peggy manfully shouldered her
burden and prepared to break up yet another home" [syn:
manfully, manly] [ant: unmanfully, unmanly]