Late 18th century; earliest use found in Thomas Twining (bap. 1734, d. 1804), classical scholar and translator. From the name of Jean-Jacques Rousseau + -ish.
Definition of Rousseauish in US English:
Rousseauish
adjectiveˈruːsəʊɪʃ
= Rousseauesque.
Origin
Late 18th century; earliest use found in Thomas Twining (bap. 1734, d. 1804), classical scholar and translator. From the name of Jean-Jacques Rousseau + -ish.