Rashi on Genesis 26:14/רש"י על בראשית כ״ו:י״ד

1וְעֲבֻדָּה רבה means a great many things to do (i. e. great undertakings) O. F. ouvraine. The word עֲבוׂדָה denotes one thing to be done whereas עֲבֻדָּה denotes many things to be done (a collective noun)