Similarly to "isch" from German, which we filed the serial numbers off of, and respelled "ish". For some reason we are squeamish about doing that to French.
Perhaps ironically, we took squeamish from French escoymous, but substituted "our" suffix.
Ok, and "-ish" and "-esque" clearly both trace back to the Proto-indo-european. So we're really just talking about spelling standards, which are a recent innovation.
Perhaps ironically, we took squeamish from French escoymous, but substituted "our" suffix.