LSJ
from Ἑκάλη, a lady who entertained Theseus, and for this received at Athens the yearly honour of the Ἑκαλήσια [ἱερά]; hence the epith. was given to Zeus as worshipped on the same day, Plu. Thes. 14.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)