Of, relating to, or suitable for epistles or letter-writing; characteristic of letters.
A variant or archaic form combining epistle with the suffix -atory (tending to or suited for), similar to formations like respiratory or explanatory. This competes with the more standard epistolary.
This is basically a linguistic synonym looking for a job—epistolatory and epistolary mean the same thing, but epistolary won the popularity contest and relegated this one to obscurity.
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