Morphology - Unit Two - Lesson No. 8
Lexical morpheme is that morpheme which has a dictionary meaning and that we can provide a definition for. For instance, happy, love, book, car, pen are all lexical morphemes because they can be found in a dictionary as independent lemmas with their own definitions and senses. Grammatical morpheme, on the other hand, is a morpheme which performs a strictly grammatical function of any type. For example, -ly, -ful, and –ness in the words happily, beautiful, and innateness are all grammatical morphemes because each one of them performs a specific grammatical function (turn this adjective into adverb, turn this noun into adjective and turn this adjective into noun, respectively).
Although a typical dictionary will provide some grammatical morphemes in the form of a separate index or as they occur in the alphabetical list, it will simply tell you the function(s) of this or that grammatical morpheme. By no means does a typical dictionary provide a definition for –ly as it does for, say, “pen” or “book” .