For adequate comprehension, second language (L2) learners need knowledge of 98% of the words in a text (Hu & Nation, 2000;Schmitt et al., 2011). However, vocabulary coverage studies used to support these findings have often excluded words such as proper nouns, 'marginal' words, acronyms/abbreviations, and compounds (e.g. 'playground').Compounds cover 1.2% of COCA corpus texts (on average), suggesting a significant role in reading comprehension (this study). Accordingly, a large 'Yes/No' test dataset (Brysbaert et al., 2021) was used to examine the degree to which 3345 compounds from Nation's 'Baseword 33 -transparent compound' list are recognized by L2 English speakers as compared to their constituent stems (i.e., 'play' & 'ground') of each compound. Results revealed that compounds are recognized as English words far less than either stem constituent. Prototypical compound examples from the results are presented, and the implications for teaching and learning, and future research are also discussed.