to detach, free, or unfasten (something from something)
3.
to break (something) apart; separate
untack in American English
(unˈtæk)
transitive verb
1.
to unfasten (something tacked)
2.
to loose or detach by removing a tack or tacks
Word origin
[1635–45; un-2 + tack1]This word is first recorded in the period 1635–45. Other words that entered Englishat around the same time include: cascade, domesticate, focus, linear, sympatheticun- is a prefix freely used in English to form verbs expressing a reversal of some actionor state, or removal, deprivation, release, etc. (unbend; uncork; unfasten; etc.), or to intensify the force of a verb already having such a meaning (unloose)