• Webster's Revised Unabridged Dictionary
    • v. t Untack To separate, as what is tacked; to disjoin; to release. "being untacked from honest cares."
    • ***
Chambers's Twentieth Century Dictionary
    • v.t Untack un-takā€² to undo what is tacked or fastened.
    • ***


Webster's Revised Unabridged Dictionary
1st pref. un-, + tack,


In literature:

Besides, I must all undress me, in a manner, to untack them.
"Pamela, or Virtue Rewarded" by Samuel Richardson
Ruyter forthwith a squadron doth untack; They sail securely through the river's track.
"Andrew Marvell" by Augustine Birrell
Leave that portion within a foot of each end untacked.
"Golden Days for Boys and Girls" by Various