From un- +‎ acknowledge.

unacknowledge (third-person singular simple present unacknowledges, present participle unacknowledging, simple past and past participle unacknowledged)

1. (rare) To not acknowledge, or to rescind acknowledgement of.
   • 1985, Mary Daly, Beyond God the Father: Toward a Philosophy of Women's Liberation, page 12:

     The servants of Method must therefore unacknowledge its nonexistence (a technique in which they are highly skilled). By the grace of this double negative may they bless its existence in the best way they know.