THACK
Etymology 1
Verb
thack (third-person singular simple present thacks, present participle thacking, simple past and past participle thacked)
(transitive) To strike; thump; thwack.
Etymology 2
Noun
thack (plural thacks)
A stroke; a thwack.
Etymology 3
Noun
thack (countable and uncountable, plural thacks)
the weatherproof outer layer of a roof, often thatch specifically
Verb
thack (third-person singular simple present thacks, present participle thacking, simple past and past participle thacked)
To cover a roof with thack.
Source: Wiktionary
Thack, Thack"er.
Definition: See Thatch, Thatcher. [Obs. or Prov. Eng. & Scot.]
Source: Webster’s Unabridged Dictionary 1913 Edition