Learning, especially in the case of language acquisition, is notan isolated process; there is ever-present competition betweenwords and objects in the world. Such competition is known toplay a critical role in learning. Namely, the amount andvariability of competing items during word learning havebeen shown to change learning trajectories in young childrenlearning new words. However, very little work has examinedthe interaction of competition amount, competitionvariability, and task demands in adults. The current studyassesses adults’ ability to map new word-referent pairs invarying amounts of competition and competitor variability. Inaddition, the effect of mapping context on retention wasassessed. Results suggest that retention is weak in some casesand importantly, there are cascading effects of competitorvariability in mapping on later retention of new words.Results are discussed in light of associative learningmechanisms and the implications of competition for learning.