eat意为“战胜”、“打败”,后接比赛中的“对手”
eg:I beat John at chess yesterday.
I can beat all runners in our school.
defeat意为“击败”.多用于指击败敌军、入侵者等,也有“使失败,使落空”等的意思
eg:We defeated the enemy in the battle.
Team A defeated(beat) Team B in the football match.
Our hopes were defeated.