Phil K

He’s too vain to wear spectacles so he squints. Combined with the way he screws his face up like a child it makes his facial features look smaller.

It’s because the im isn’t a prefix but part of the word. (It was originally spelt empeche)

It is, check the OED.

Look up Egg Theory. It will blow your mind.

Basis becomes Bases Crisis becomes Crises Oasis Oases Echolalia Echolalies Etc Generally the vowel becomes an e

Illinois Illinoes