WTW for a word that is almost exclusively only used in a set phrase? For example, the word “figment” in the phrase “a figment of your imagination”.
byu/DracoOccisor inwhatstheword

Bayoris
https://en.wikipedia.org/wiki/Fossil_word

DracoOccisor
Solved

aj-uk
I hope you feel gruntled.

Reapr
and whelmed

From wikipedia:

“Born fossils”
These words were formed from other languages, by elision, or by mincing of other fixed phrases.

caboodle, as in “kit and caboodle” (evolved from “kit and boodle”, itself a fixed phrase borrowed as a unit from Dutch kitte en boedel)
druthers, as in “if I had my druthers…” (formed by elision from “would rather”[11] and never occurring outside this phrase to begin with)
tarnation, as in “what in tarnation…?” (evolved in the context of fixed phrases formed by mincing of previously fixed phrases that include the term “damnation”)
nother, as in “a whole nother…” (fixed phrase formed by rebracketing another as a nother, then inserting whole for emphasis; almost never occurs outside this phrase)