This inquiry explores whether bilinguals activate lexical knowledge from both their dominant first language (L1; Spanish) and their less-dominant second language (L2; English) during novel third language (L3; Slovak) word learning. Moreover, it explores the extent to which L2 activation in L3 lexical learning depends on the level of L2 proficiency. This study contributes to the inquiry of the degree of language dominance and its implications for L3 lexical learning and parallel activation of multilinguals’ languages.