AbstractIdiom studies typically consider variables such as familiarity, decomposability and literal plausibility, and the contributions of these to how figurative phrases are processed are well established. In this study we consider the effect of a previously untested variable: semantic richness. Semantic richness refers broadly to the range of semantic information denoted by a lexical item, and reflects features such as imageability, number of senses, semantic neighbourhood, etc. This has generally been restricted to single words and sometimes to metaphors, so here we investigate how some aspects of this measure – specifically those reflecting perceptual characteristics – contribute to the processing of idiomatic expressions. Results show that aspects of semantic richness affect idiom processing in different ways, with some (emotional valence) contributing to faster processing of figuratively related words, and others (those that highlight physical and literal aspects of the idiom) showing an inhibitory effect. We also show that for some of the dimensions of semantic richness considered here, there is a significant correlation between a measure constructed from the ratings of component words, and one gathered from ratings for the phrase as a whole, suggesting a straightforward way to operationalise semantic richness at a multiword level.