aglǣca, m.n: hostile fighter, fierce combatant. (AH-GLACK-ah / ˈa-ˌglæː-ka)

There aren’t any good word-for-word translations. Often translators use ‘monster’ but there is no word in Old English that means simply ‘monster’, and aglǣca can refer to (human) heroes as well as monsters. Grendel is an aglǣca but so is Beowulf.