Early 17th century; earliest use found in Thomas Adams (1583–1652), Church of England clergyman. From classical Latin epistolicus or its etymon ancient Greek ἐπιστολικόςepistolic + -al.
Definition of epistolical in US English:
epistolical
adjectiveˌɛpɪˈstɒlɪkl
literary
Epistolary.
Origin
Early 17th century; earliest use found in Thomas Adams (1583–1652), Church of England clergyman. From classical Latin epistolicus or its etymon ancient Greek ἐπιστολικός epistolic + -al.