|Ah, sorry - I read "Cornwall" for "Cromwell". The Cromwell link I simply don't believe, sorry. At least, not without some substantiation. I can't find a usage of the word recorded before 1811, and K-C C stops at 1789.|
The "try singing it on the streets of Dublin" argument doesn't really wash, either, I'm afraid. I would be pretty careful about where I say "niggardly", but that doesn't make the word offensive, merely open to being heard as offensive.
In this song, inasmuch as one can tease sense out of the nonsense, the "knick-knack" is possibly rapping of the knuckles, in which case the action described is probably a rapping of the knuckles followed by a blow. Alternatively, possibly something to do with food? Knucklebones, backstrap, bone... I think the former is probably closer.
Have to say, though, I think that Triplets' response to PW was unnecessarily dismissive - in this case, I don't think that you're right, and will continue not to believe that you're right, and object very strongly to being told that I am trying to justify discrimatory language without any corroboration that the language is in fact discriminatory, but we shouldn't dismiss such concerns out of hand on Barbelith.