ETYM Greek, a widening, an opening; ana up + euros wide.
A soft, pulsating, hollow tumor, containing blood, arising from the preternatural dilation or rupture of the coats of an artery.

Abnormal swelling of blood vessel. A sac-like widening of a blood vessel.
Weakening in the wall of an artery, causing it to balloon outward with the risk of rupture and serious, often fatal, blood loss.
If detected in time, some accessible aneurysms can be repaired.