Entries linking to ruttish
"periodically recurring sexual excitement in animals; animal mating season" (originally of deer), early 15c., from Old French rut, ruit, from Late Latin rugitum (nominative rugitus) "a bellowing, a roaring," from past participle of Latin rugire "to bellow" (from PIE imitative root *reu-). If so, the notion is of the noise made by deer at the time of sexual excitement. The noun rut "roar of the sea" (1630s) in Scottish and persisting in New England dialect is of uncertain connection.
The -ish in verbs (abolish, establish, finish, punish, etc.) is a mere terminal relic from the Old French present participle.