Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
shrink 2 (v.)
The Standard past tense is usually shrank but occasionally shrunk, and the past participle is always shrunk, with the participial adjective usually shrunken: She shrank [shrunk] from telling him. The market for shrunken heads has shrunk. Shrank as past participle, as in This sweater has shrank, is Vulgar and a shibboleth.
