Iconicity (the resemblance between form and meaning) exists in various modes of communication. This study investigated whether adults interpret iconicity in speech and gesture via a modality-independent ability. We tested 348 adult participants and assessed their ability to use iconic prosody and iconic gesture cues when interpreting novel verb meanings. We manipulated the rate of the spoken novel verbs (iconic prosody) and the rate of observed hand movements (iconic gestures) to be either fast or slow in two verb-action matching tasks. Adults could use these iconic speed cues to interpret novel verbs as referring to a fast or slow version of the same action. Adults showed similar performances in the two verb-action matching tasks: those who performed well in the iconic prosody task also performed well in the iconic gesture task. This positive correlation persisted even after controlling verbal working memory. Thus, we conclude that adults possess a modality-independent ability for interpreting iconicity.