Definitions (by source)
a track, a trail (orig. v.n. of aithlenaim, I follow, pursue). In late literature usually found in the stereotyped phrases a haithle, d’aithle, ‘after,’ as a haithle sin ‘after that’ ; note a aithle, 3944. The earlier meaning in: d’aithle a hálaidh, from the track of her wound, 2588. ; fear aithle, a tracker 3517, fian aithle, tracking warrior bands, 3445.
in phr. as a ha., ‘thereafter,’ 5355