Managed to recognise that it was "chemist" with "cat" inserted, but that felt more as if it was an answer than a clue (except that "checatmist" only appears on the web once - a one word Googlewhack - and it's the same clue, only the middle word has three letters).

And having seen the answer, my excuse for not solving it immediately is that it should have been "pharmcatacist"....