Same entry in ps.-Zonaras; similar one (but with the headword spelled with double lambda) in e.g. Hesychius kappa3347.
This rare word is attested elsewhere as a foodstuff for sick horses, but in Palladius' Life of Chrysostom it refers to the food of a monk (PG 47.71; see Lampe s.v.), and Adler mentions the role of kollyva in the hagiography of St. Theodore the Tyro, citing DuCange s.v. According to the story, in the first week of Lent the emperor Julian ordered all the bread sold in the marketplace to be contaminated with the blood of sacrificed animals; St. Theodore appeared in a dream to the patriarch of Constantinople, Eudoxius, and told him to instruct the people not to buy bread but to eat only boiled wheat grains. See web address 1 (February 17).
Nowadays the word is applied to boiled wheat (sweetened and spiced) used at memorial services for the dead. This usage is attested from Byzantine times: see Wikipedia entry at web address 2.