1680s; see April + fool (n.). April-gowk (from Old Norse gaukr "a cuckoo") is a northern variant. April Fool's Day customs of sending people on false errands seem to have come to England from France late 17c.; originally All Fool's Day (1712). In Cumberland, Westmorland and northern parts of Lancashire and Yorkshire, however, May 1 was the day for hoaxing, and the fool was a May gosling. That custom is attested by 1791.
"the order being changed," c. 1600, Latin, from vice, ablative of vicis "a change, alternation, alternate order" (from PIE root *weik- (2) "to bend, to wind") + versa, feminine ablative singular of versus, past participle of vertere "to turn, turn about" (from PIE root *wer- (2) "to turn, bend"). "The phrase has the complete force of a proposition, being as much as to say that upon a transposition of antecedents the consequents are also transposed" [Century Dictionary].