There is a growing awareness in the NLP community of the problems that Multiword Expressions (MWEs) pose and the need for their robust handling. MWEs include a large range of linguistic phenomena, such as phrasal verbs (e.g. "add up"), nominal compounds (e.g. "telephone box"), and institutionalized phrases (e.g. "salt and pepper"). These expressions, which can be syntactically and/or semantically idiosyncratic in nature, are used frequently in everyday language, usually to express precisely ideas and concepts that cannot be compressed into a single word.
Ivan A.Sag et al.: Multiword Expressions: A Pain in the Neck of NLP (2002) in: LECTURE NOTES IN COMPUTER SCIENCE, Vol. 2276, p. 1-15.