Dictionary entry

κῆτος

G. Abbott-Smith's A Manual Greek Lexicon of the New Testament with Strong's

κῆτος, -εος (-ους), τό,

[in LXX: Jh 2:1, 11 (דָּג), Ge 1:21 (תַּנִּין), etc.;]

a huge fish, sea-monster: Mt 12:40^(LXX).†