Although retrieval of lexical forms is a prerequisite for language production, research of L2 vocabulary learning has focused much more on meanings and form-meaning mappings than on development of detailed, accessible mental representations of forms. This is particularly true with respect to multi-word items (MWIs). We report an experimental study involving a variety of intra-lexical, usage-based, and interlingual co-determinants of L2 vocabulary learnability pertaining to MWIs. Each learner (N = 60) encountered a randomly allocated set of 26 two-word MWIs (Nsets = 4) semi-randomly drawn from a larger pool of MWIs. Learners were asked to remember either the 13 MWIs showing the form variable assonance (e.g., "change shape") or the 13 nonassonant control MWIs (e.g., "sound good"). Posttests of form recall revealed a large, durable effect of the focusing task in combination with forewarning of testing. Except when MWI concreteness (a semantic variable) was high, assonance had a positive effect on retrievability in recall tests given after delays of 15 minutes and one week. There was a consistent effect of the semi-semantic variable Mutual Information. Even in the context of a strong focus on forms, form variables are not the only variables that matter.