Archaic past tense of acknowledge, meaning to admit, recognize, or confess something.
From acknowledge (from ac- + knowledge), with -new as an archaic past tense formation, showing Old English strong verb patterns that survive in few words today.
This verb form is basically dead, replaced by 'acknowledged,' but it shows how English once had dozens of past tense forms like 'knew,' 'grew,' 'blew'—and acknew followed that same pattern.
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