an element of a construction that cannot be further divided into grammatical constituents: the morphemes of an utterance are usually considered to be its ultimate constituents.
Compare immediate constituent.
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British Dictionary definitions for ultimate constituent
a constituent of something, such as a linguistic construction, that cannot be further subdivided in the terms of the analysis being undertakenCompare immediate constituent
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012