A non-committal gloss on this epic adjective, the etymology of which was a matter of dispute amongst ancient scholars: either "great in respect of hollows" (from the adjective khtw/eis, itself less than self-evident in meaning but best-known as the epic epithet of Lakedaimon) or "great in respect of sea-monsters" (from the noun kh=tos: see kappa 1555). For passages see LSJ s.v. (web address 1).
cf. (e.g.) Etymologicum Magnum 574.42 and the scholia to Homer, Iliad 8.222.