From The Collaborative International Dictionary of English v.0.48 [gcide]:
Passably \Pass"a*bly\, adv.
Tolerably; moderately.
[1913 Webster] Passacaglia
From WordNet (r) 3.0 (2006) [wn]:
passably
adv 1: to a moderately sufficient extent or degree; "pretty
big"; "pretty bad"; "jolly decent of him"; "the shoes are
priced reasonably"; "he is fairly clever with computers"
[syn: reasonably, moderately, pretty, jolly,
somewhat, fairly, middling, passably] [ant:
immoderately, unreasonably]