I think there are 2 views here that are being combined in this entry. There are linguists that would only include as morphemes, a unit of "grammatical meaning," like pural markers, past tense markers etc. Others would include as morphemes, any unit of "meaning," like "find," "book," etc. In introducing "meaning" into the concept of morpheme, one also introduces a subjective element and context-sensitive element.
I am not sure that one can combine these approaches.
Dictionary definitions are rarely helpful here.
I'm also very leary of combining Morphological analysis and Lexical analysis, as is implied by saying morphemes combine to form lexemes. We are definitely treading too far from the Neutral Perspective in that statement. I know linguists (non-Chomsky to be sure) who would read this and consider it an aberration.