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Webster 1913 Edition

Verb.

[1st pref.

un-

tack

To separate, as what is tacked; to disjoin; to release.

being

untacked

from honest cares.

Barrow.

Verb.

To separate what is tacked; to disjoin; to loosen what is fast.

untack ‎(third-person singular simple present untacks, present participle untacking, simple past and past participle untacked)