In Gaelic the spelling of nouns (including names) can change in response to their grammatical case. The "starting point" is the nominative case but in the genitive/possessive case the noun is aspirated/lenited (indicated by inserting an H and after the first consonant and inserting an I after the last vowel). So, "mac" (son of) in the genitive case becomes "mhic", pronounced VIC and often shortened to 'ic. Of course, there is no letter H in the Gaelic alphabet and its use in printing takes the place of the aspiration (exhaling) mark. This is a subject in itsself, and one in which i am far from expert. MacNish could be a surname for some people. They do not appear to have used surnames except in formal/legal contexts and most people were identified/referred to in conversation by an eke name, the most common of which was a patronymic. If you send me your email by PM, I will try to find a paper I wrote on this topic some years ago and forward it to you.
Ian
