what is the definition of steam
steam noun [U]. B2 the âhot âgas that is âproduced when âwater âboils: Steam ârose from the âsimmering âstew. steam âturbines a steam âengine/âlocomotive the âage of steam (= the âperiod when steam âprovided âpower for ârailways and âfactories) The âpump is âdriven by steam.