1. convenient, suitable, agreeable ...c1300 obs.
2. handsome, comely, graceful; pleasant ...1340 obs.
that which suits one; convenience, purpose ...c1400 obs.
from Old French avenant, present participle of avenir (to arrive, happen, succeed, to suit, befit, become), from Latin advenīre (to come, to arrive, to reach), from ad- (to) + venīre (to come)
FIRST DOCUMENTED USE
c1300 - see EXAMPLE below
"...Anothir folk ther is, stronge men and foule
They buth long, and blak, and lokith as an houle.
They no haveth camayle, no olifaunt,
No kow, no hors, avenaunt.
On hand they creoputh, at o word,
They n'ul have non othir lord..."
From: Kyng Alisaunder
(A long and sophisticated thirteenth century romance poem, written in Middle English, about the life of Alexander the Great)