verb (~ed; ~ing) Date: 15th century transitive verb to make stiff or stiffer, intransitive verb to become stiff or stiffer, ~er noun
STIFFEN
Meaning of STIFFEN in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012