1. The word, erogate, appears to have the same root word as derogate/ interrogate/ abrogate/ arrogate, etc. Onelook confirms it to be the Latin, rogare, to ask. How did erogate come to acquire its association with money? And if derogate and erogate both trickled down with their Latin prefixes intact, why, despite sharing a common root and similar-meaning prefixes, are they two completely disconnected words in current usage?

2. Why is 'subter' the prefix and not, a simple, 'sub'? To my mind, 'subter' is a Latin prefix with a distinct connotation of, something unknown or secretive. Why is it used as the antonym for supererogatory?

Lovely words. wwh and tsuwm, thank you.