adj

• (linguistics) Conveying the speaker's emotions and/or attitudes, in addition to the denotative or literal meaning.
  "These adults performed significantly more poorly than a group of 28 control adults on all measures of articulation and expressive and receptive language."
• (programming) Able to represent a number of ideas or concepts.
  "A programming language that is Turing complete is more expressive than one that is not."

noun

• (linguistics) Any word or phrase that expresses (that the speaker, writer, or signer has) a certain attitude toward or information about the referent.
  "Consider the case of expressives, where no prior knowledge of the speaker’s attitudes are required to interpret the utterance. In (43) ["That jerk Alexa keeps making me look bad"], Steve does not need to know (and in fact has no prior knowledge of) anything relating to Siri’s attitudes towards Alexa to interpret that Siri has a negative attitude about Alexa. It is the expressive that jerk that implies the negative attitude."
• (linguistics, more narrowly) A word or phrase, belonging to a distinct word class or having distinct morphosyntactic properties, with semantic symbolism (for example, an onomatopoeia), variously considered either a synonym, a hypernym or a hyponym of ideophone.
  "Cross-linguistically 'expressives' are more commonly termed 'ideophones' [...] Expressives are often cited as a distinctive shared feature of the Austroasiatic language family (Diffloth and Zide 1992; Osada 1992 (Mundari); Svantesson 1983 (Kammu)). [...] I do not make a distinction between expressives and ideophones. [...] I distinguish expressives from onomatopoeic forms, although the two probably overlap."