What is it called when a word's derivitave survives its defunct root word?

The best instance I can think of is “disgruntled”. “Gruntle” is either archiac or out of common use.

Also…

“gormless” (gorm?)
“uncouth” (couth?)
“feckless” (feck?)

Is there a linguistic term for this? And are there any other words that fit that term?

“Nonchalant” is another example, and it’s more interesting since it’s a negative word that has outlived its positive.

And decapitated.

Couth is from an Old English word meaning ‘known’.
Feck is from Scottish dialect, a shortened form of “effect.”
Gorm was never a word apart from being an element in the whimsical coinage “gormless,” AFAIK.

Gorm apparently was a word . . . sort of.

From Dictionary.com

I hate to post twice in a row like this, but it seems that chalant never was an English word to begin with.

Again, from Dictionary.com

And from their word history in the entry:

So it appears that we borrowed nonchalant directly from French without also borrowing the positive from which it derives. Man, I love etymology.

Capitation lives on though - as a form of taxation and (usually medical) remuneration.

“Uncanny” from the Scots “canny” for “natural.”

This thread is whelming.

Well thank you…I think.

Canny is a living word. It means shrewd.