Which one is the original prefix: con-, com-, or cor-?
Solution 1:
Con- derives from the Latin prefix con-, which was in turn derived from the Latin word cum "with".
The prefix was assimilated to a following sound according to the following rules:
- Before vowels and h, the prefix becomes co-.
- Before b, m and p, the prefix becomes com-.
- Before l, the prefix becomes col-.
- Before r, the prefix becomes cor-.
- Before n or gn, the prefix becomes cō- (or con- in Late Latin).
- Before gn, the prefix becomes co-.
- Before s or f, the vowel in the prefix becomes nasalized con- [kõ]ː