Maybe I am making a mountain out of molehill but analyzing the word structure to see which words have an "ain" suffix is driving this relatively new novice batty. 
Is the <-ain> suffix archaic at this point. I am having a hard time determining which <ain> morphemes are suffixes and which are part of the base word. I saw it listed with one of my words but now I can't find it. 
I'm getting lost in the Latin and etyomonline doesn't have it listed as a suffix in the few <ain> words there are. 
I tried making word sums and looking for other words with the base. The only one of which I am sure is <certain> where we have words like certify, certificate, 
Here are some words: mountain, <mas> is the same root for mountain and mount; bargain (I can see its relation to barge but etymonline says it is a suggestion that it comes from barge but the meaning of bargain and barge seem to carry the same meaning like embargo), captain has many relatives..non of which include a possible word sturcture of <capt> so I think that's out.