The vowel exchange "a" to "o"

[Jorge_Stolfi]

If you are looking for a more consistent exchange between two characters in the VMS then the answer is with t and k . Unlike the Italian examples that exchange at the end of a word for grammatical reasons, t and k in the VMS exchange mid-word, rarely at the end of a word.

In the Semitic or Afro-Asiatic languages (which include Arabic, Hebrew, and Ge'ez), words are inflected by changing their vowels while keeping the consonants fixed.

Even in Indo-European languages inflections sometimes change phonemes way back inside the stem. For example in Italian you have "cAnto" ("I sing", with stress on "a" and closed "o") and "cantÒ" ("he sang", with stress on the open "ò"); or "bEllo" ("nice", with stress on open "e") and "bellIssimo" ("very nice", with closed "e" and stress on the "i"). 

But just because two words differ in only one letter or phoneme it does not mean that they are related.  Consider  "is", "if", "it", "in", or "thug", "thud", "thus", "this", "thin", "then", "them", "they", ...

All the best, --stolfi