An example is "huckle", as in "huckleberry". The word itself isn’t actually a word, it’s a bound root morpheme.
This requires a brief lesson in linguistics.
A morpheme is the smallest unit of meaningful language. "Girl" is a morpheme, as is "skip." "Girlfriend" has two morphemes, as does "skipper".
Some morphemes can be free (as in girl, skip, and type) whereas other morphemes are bound (as in huck, funct, and ept).
A free morpheme has meaning, a bound morpheme does not. In order to make the bound morphemes make sense, you have to add another morpheme. Funct must become defunct and ept must become inept. So, to review, there are free morphemes and bound morphemes.
A free morpheme can stand alone, and a bound morpheme must be attached to another morpheme before it makes sense.