| Definition -
A morpheme that cannot stand alone as a word.
Note: A morpheme that CAN stand alone as a word is called a free morpheme.
Example - The word undone has two morphemes:
(1) the bound morpheme un- and
(2) the free morpheme done.
Oxford English Dictionary - The concept's first citation is from 1948:
"If it is a bound form, the element must — in order to be a morpheme — be active."
(Word Apr. 20)