Vocabulary is the general term for words in a language. Morpheme is a meaningful unit in a language. Vocabulary words are always either single morphemes or made up of multiple morphemes. Morphemes are the building blocks of vocabulary words. For example the vocabulary word "dog" is made up of a single morpheme. "Dog" is a meaningful unit. When you hear or see those three letters/sounds together in English you know what it means. It signifies something meaningful. You probably have or can conjure up a picture of what those three letters/sounds when put together mean. This is an example of a free morpheme. It is a meaningful unit and it can stand alone. It doesn't need anything else attached to it.
Using the same example if we add "s" to it; dogs. Now the vocabulary word is made up of two morphemes /dog/ and /s/. "S" is a morpheme when it is used to make singular words plural. "S" definitely is meaningful to speakers of English. When you see or hear that ending added to words you know it means "more than one of" the thing. The vocabulary word "dogs" is made up of two morphemes. The /s/ in dogs is called a bound morpheme. In other words it can not be used by itself. It must be attached to a free morpheme, in this case, dog in order to function as a morpheme; that is, carry meaning.
From this example you can see that all vocabulary words are made up of morphemes either a free morpheme or a vocabulary word made up of a free morpheme with one or more bound morphemes attached to it. Each of the bound morphemes will be meaningful. Native speakers of the language will know exactly what they mean.
Free morphemes are always vocabulary words. Bound morphemes are never vocabulary words; that is, they can never stand alone. They must always be attached to a free morpheme.
