This study examined interactions of word and learner characteristics during foreign vocabulary learning, focusing on translation ambiguity and individual differences in cognitive resources and linguistic background (language proficiency, multilingual experience). Fifty-three native Hebrew speakers and Russian-Hebrew multilinguals learned the phonological form of target Arabic words along with their Hebrew translations and definitions. The mapping could be translation ambiguous, with a single Hebrew word translated into two Arabic words (one-to-many) or translation unambiguous (oneto-one mapping). Results from translation production and meaning recognition tests revealed that translation-ambiguous words were more difficult to learn than translationunambiguous words. This disadvantage did not dissipate with time, and learners' phonological short-term memory was associated with increased translation ambiguity costs. Learners' proficiency in the language through which learning took place (Hebrew), but not degree of multilingualism, modulated learning. Findings underscore the importance of item and learner interactions, clarifying the multilingualism effect in novel language learning. active competition between the different alternative translations may hinder performance, which is in line with assumptions of competitive inhibitory interactions between connected representations in interactive activation models (Doherty, 2004;McClelland & Rumelhart, 1981). Second, translation-ambiguous words may suffer from a decrease in associative strength, similar to the fan effect (e.g., Anderson, 1974). The fan effect assumes that as more facts are associated with a concept, each fact has decreased probability of occurrence and thus lower associative strength. As a result, the more facts that are connected to a concept, the longer individuals take to recall the concept. In the case of translation-ambiguous words, a learner would take longer to retrieve a translation if additional translations are linked to the same word.The majority of previous studies have examined the one-to-many direction of ambiguity, where a single L1 word was mapped onto two foreign language vocabulary items (for an exception focusing on many-to-one mapping, see