High ceilings and ingenuine allies:tapping into the idiom meaning knowledge of first and second language speakers of English

Idioms are undoubtedly important for second language (L2) learners, who encounter them in instructed learning, textbooks/resources and in out-of-class language use. While research on first language (L1) and L2 idiom comprehension shows how well L1/L2 speakers understand various idioms and the role of different predictors, important questions remain about how knowledge varies with more difficult task types and stimuli, how well L1 ‘norms’ serve L2 learners, how subjective and objective predictors of idiom knowledge interact and how L2 learner inferencing works in learning idioms. To address these issues, university-age L1 and L2 English (L1 German) participants provided meaning descriptions and familiarity ratings for 100 challenging idioms from learner resources, and each idiom was assigned an OpenAI-generated transparency rating, corpus-based frequency and to one of six cross-language overlap (CLO) types. Descriptive statistics showed lower and more varied idiom meaning knowledge than might be expected, especially for the L1ers, who were some way off ceiling level. Mixed-effects regression revealed familiarity and transparency as positive L1 and L2 knowledge predictors, but groups differed in sensitivity to idiom frequency, which only mattered for the L1ers and CLO, which (as expected) only mattered for the L2ers, who mistook false friends as genuine allies.