A morpheme is the smallest meaningful unit of a language. While a morpheme may not stand alone as a word, it adds unique meaning to the word. For example, adding "-s" pluralizes a word, which changes the meaning even though it isn't a word by itself. The only thing smaller that a morpheme could be divided into is individual letters (or sounds) that lack meaning.
Often, multiple morphemes are used together to form words, though some words are comprised of a single morpheme. For example: The word “homecoming” is made of three morphemes (home, com[e], -ing). However, the word “can” is a single morpheme. Not all morphemes are full words on their own, but all make meaning. Some morphemes are placed at the beginning or end of words to alter the meaning (known as “affixes”), such as the suffixes "-s" and "-ed" and the prefixes "re-" and "un-".
Morphemes Versus Syllables
A syllable is a unit of pronunciation with one vowel sound. Some words have just one syllable, while others are made up of multiple syllables. Unlike a morpheme, a syllable does not have to make meaning.
For example: The word “responsible” has four syllables (re-spon-si-ble). However, the word “hat” has only one syllable. While “understanding” has four syllables (un-der-stand-ing), it has two morphemes (understand-ing); “happy” is a two syllable word (hap-py) but has one morpheme.