FenMarsh; swamp.Behold now behemoth, which I made with thee; he eateth grass as an ox. He lieth under the shady trees, in the covert of the reed, and FENS. ( Job 40:15 Job 40:21 ) Source: A King James Dictionary. (Used with permission. Copyright © Philip P. Kapusta) Bibliography Information"Entry for 'Fen'". A King James Dictionary.