The Irish or Gaelic origin of the word tinker remains a slight possibility, but
the evidence from early English records might suggest otherwise. The word
tinker is found in English as early as the 13th century, and the Northern form
tinkler, even earlier in the 12th.
Here is what Onions says in the _Oxford Dictionary of English Etymology_:
"perhaps repr. Old English *_tinecere_, from *_tinecian_ work in tin, from
_tin(n)_ TIN, with _k_-formative as in _smearcian_ SMIRK; but the appearance of
synonymous (northern) _tinkler_ at an earlier date (XII) is them difficult to
tinkler is equally difficult to account for if the word derives from tin-ceard.
Irish tinne is a borrowing from English, but as I don't have an Irish
dictionary here, I can't say how early it is. I suspect it is a borrowing
somewhat later than the 12th or 13th century, and therefore after the formation
of the word tinker, but I stand ready to be corrected on this.