Lexicology

 The main unit of the lexical system of a language resulting  from the association of a group of sounds with a meaning is a word. This unit is used in grammatical functions characteristic of it. It is the smallest language unit which can stand alone as  a complete utterance.

A word, however, can be divided into smaller sense units - morphemes. The morpheme is the smallest meaningful language unit. The morpheme consists of a class of variants, allomorphs, which are either phonologically or morphologically  conditioned, e.g. please, pleasant, pleasure.

Morphemes are divided into two large groups: lexical morphemes and grammatical (functional) morphemes. Both lexical and grammatical morphemes can be free and bound. Free lexical morphemes are roots of words which express the lexical meaning of the word, they coincide with the stem of simple words. Free grammatical morphemes are function words: articles, conjunctions and prepositions ( the, with, and).