n. — Newfoundland
a person who browses in a store and does not buy anything; a window-shopper.
Type: 3. Semantic Change — The EDD lists the definition of the verb twack as 'to turn quickly; to change one's opinion' and marks it as obsolete (see EDD, s.v. "twack"); it is possible that the nominal meaning of twack in Newfoundland and Labrador English, namely 'a window-shopper', derives from this meaning. Accordingly, a person who twacks (see meaning 2) is seen as someone who is "unable to make up [his or her] mind on simple choices" (see the 1990 quotation). Thus, twack may be both a preservation and semantic change from this British English meaning. Note that the earliest attestation is in its nominal form (see the 1919 quotation). The EDD classifies the term as obsolete (see EDD, s.v. "twack") - around 1900 - which is an argument for a semantic change in Newfoundland English of a term that, in England, was on its way out. NLE is considered as conservative, (see, e.g., Clarke 2010b: 102-103), yet this example shows the innovative potential that is inherent in any variety, no matter how traditional it may be.
See also DNE, s.v. "twack" (n), EDD, s.v. "twack", labels the term as "Obs." and "e.An" (East Anglia).
2 v., verbal n. — Newfoundland
to browse in a store without buying; to window-shop.
Type: 3. Semantic Change — Based on written attestations, it appears the the verb "to twack" is derived from the noun (see meaning 1), via the process of conversion. Note that the action of twacking is stated to be more fitting for a leisurely occasion (see the 2005 quotations) with time to spare (e.g on a weekend) (see NL Tourism reference).
See also DNE, s.v. "twack" (v).