On the Definition of Word is a 1987 book by Anna Maria Di Sciullo and Edwin S. Williams in which the authors examine the notion of word in linguistics. They distinguish four concepts of "word": listemes, morphological objects, syntactic atoms, and phonological words. The authors' main claim is that there is a strict distinction between syntax and morphology.
^Carstairs, Andrew (March 1989). "Anna-Maria Di Sciullo and Edwin Williams, On the definition of word (Linguistic Inquiry Monographs 14). Cambridge, Massachusetts: MIT Press, 1987. Pp. x + 118". Journal of Linguistics. 25 (1): 225–229. doi:10.1017/S0022226700012184. S2CID145466232.