I think you are onto something with ‘tailor’. If we take it as the verb ‘to tailor’ that is the synonym of the ‘to fashion’. Tailor as a profession is not a synonym of the noun ‘fashion’. But it is enough for them to be synonyms in one sense. So that works.
I hear you on ‘cat’ but i wouldn’t call that relationship synonyms.
To fashion something is to make something. To tailor something is to customise it.
`cat` is a Unix command for concatenating files, which you could argue is fusing them together?