Motivated by accounts of concept use in autistic spectrum disorder (ASD) and a computational model of weak central coherence (O'Loughlin and Thagard, 2000) we examined comprehension and production vocabulary in typically-developing children and those with ASD and Down syndrome (DS). Controlling for frequency, familiarity, length and imageability, Colorado Meaningfulness played a hitherto unremarked role in the vocabularies of children with ASD. High Colorado Meaningful words were underrepresented in the comprehension vocabularies of 2- to 12-year-olds with ASD. The Colorado Meaningfulness of a word is a measure of how many words can be associated with it. Situations in which high Colorado Meaningfulness words are encountered are typically highly variable, and words with High Colorado Meaningfulness often involve extensive use of context. Our data suggest that the number of contexts in which a particular word can appear has a role in determining vocabulary in ASD. This suggestion is consistent with the weak central coherence theory of autism.