In Nouns^x, Consonants^x, Prefixes^x

I don't know of a site like that. Initial s is pronounced /s/, except in sure and sugar , where it is pronounced /S/*. Medial s is problematic. There are no hard-and-fast rules -- mostly just lists. In -ssion or -ssure, the double S is /S/. impression, pressure In -sion or...

There are many rules governing the writing of compounds, and many exceptions to the rules. I would say that you should always first consult a good dictionary to see if the compound has an established form. From Webster's Third New International Dictionary , here are some of the rules governing...

There is no rule. Words with these prefixes have come about through accidents of history. The most usual is "un-", but always consult a dictionary. The following does not really answer your question, but you may find it somewhat useful anyway, especially if you're willing to work to dig some of...