The Collaborative International Dictionary of English v.0.48:

Unacknowledged \Unacknowledged\
   See acknowledged.

WordNet (r) 3.0 (2006):

unacknowledged
    adj 1: not recognized or admitted [ant: acknowledged]
    2: not openly acknowledged; "an unacknowledged emergency"

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "unacknowledged":
   anonymous, cryptonymic, cryptonymous, forgotten, ignored,
   ill-requited, ill-rewarded, incognito, innominate, nameless,
   neglected, uncredited, undefined, undesignated, unfairly neglected,
   unidentified, unknown, unnamed, unrecognized, unrequited,
   unrewarded, unspecified, unthanked, without a name