Definition of "compositional"

A wet súit meaning a suit that is wet is a compositional phrase; a wét suit meaning a garment worn by skin divers is a compound.

1979, Edward S. Klima, Ursula Bellugi, The Signs of Language, page 202

We have already noted that compounds tend to have meanings that are not entirely compositional and would therefore need to be listed.

2003, Jean Boase-Beier, Ken R. Lodge, The German Language: A Linguistic Introduction, page 153

Sentence meaning is compositional because, to a large extent, it depends on a combination of the meanings of sentence constituents, which implies the concept of semantic structure.

2004, Sergei Nirenburg, Victor Raskin, Ontological Semantics, page 106

To cite a textbook example, white house and White House are both written with internal spaces, but the first is argued to be a phrase because it is semantically compositional and has phrase-final stress, while the latter is argued to be a word because it has noncompositional semantics and compound-initial stress.

James Myers, Wordhood and Disyllabicity in Chinese