Just a rule of thumb from my perspective (compound words are not included), such as th/t/s/z/c + /V/ + n/m:

> 
> *T-*
> 
> 
> **-tion/-sion** (question, division, conclusion),
> 
> 
> *TH-*
> 
> 
> **-than** (leviathan),
> 
> 
> **-thon** (marathon, python),
> 
> 
> **-thm** (algorithm, rhythm),
> 
> 
> **-thom** (fathom),
> 
> 
> **-them** (anthem),
> 
> 
> *S-*
> 
> 
> **-sm** (apriorism, prism),
> 
> 
> **-san** (artisan, courtesan, partisan, ptisan),
> 
> 
> **-son**(bison, prison, season),
> 
> 
> **-som**(blossom, bosom, ransom, transom),
> 
> 
> *Z-*
> 
> 
> **-zan** (azan, bartizan),
> 
> 
> **-zen** (citizen, dozen),
> 
> 
> **-zam** (Nizam),
> 
> 
> **-zem** (chernozem, diltiazem),
> 
> 
> **-zon**(horizon, Amazon, menazon, blazon, cabezon),
> 
> 
> *C-*
> 
> 
> **-can** (florican, pecan, pelican, toucan),
> 
> 
> **-cam** (piroxicam).
> 
> 
>