"It was a mistake any wizard could make
Who was tired and caught on the hop
One piffling error, and then, to my terror,
I found myself facing the chop."
-- Nearly-Headless Nick (JKR)
On the evening of 30th October, 1492, Lady Grieve, a Lady-in-Waiting in the court of King Henry VII (Pm), encountered Sir Nicholas deMimsey Porpington while “a-strolling the park in the dusk” and asked him for help straightening her teeth (JKR). His spell went awry, and Lady Grieve found herself sprouting a tusk. Instead of allowing him to repair the damage, the authorities clapped him in jail and attempted to behead him the next morning. Sadly, the executioner’s axe was blunt and it took forty-five whacks to kill poor Nick, and even so his head was never completely removed. The fate of Lady Grieve’s tusk was never disclosed.
Commentary
Etymology
"grieve" = to feel great sadness and distress. Nick may be using the name descriptively rather than using the real name of the woman involved ("Lady who caused me grief"), in the same way that Benedict in Shakespeare's Much Ado About Nothing refers to Beatrice as "my dear Lady Disdain" because she was disdainful of men in general and of him in particular.
Notes
Rowling wrote on her original website (JKR):
In the first draft of 'Chamber of Secrets', Nick sang a self-penned ballad explaining how his head had (nearly) come off. My editor was not very fond of the song and so I cut it. However, for those who are curious, here is the story of Nick's decapitation in his own moving words.
It was a mistake any wizard could make
Who was tired and caught on the hop
One piffling error, and then, to my terror,
I found myself facing the chop.
Alas for the eve when I met Lady Grieve
A-strolling the park in the dusk!
She was of the belief
I could straighten her teeth
Next moment she'd sprouted a tusk.
I cried through the night that I'd soon put her right
But the process of justice was lax;
They'd brought out the block, though they'd mislaid the rock
Where they usually sharpened the axe.
Next morning at dawn, with a face most forlorn,
The priest said to try not to cry,
"You can come just like that, no, you won't need a hat,"
And I knew that my end must be nigh.
The man in the mask who would have the sad task
Of cleaving my head from my neck,
Said "Nick, if you please, will you get to your knees,"
And I turned to a gibbering wreck.
"This may sting a bit" said the cack-handed twit
As he swung the axe up in the air,
But oh the blunt blade! No difference it made,
My head was still definitely there.
The axeman he hacked and he whacked and he thwacked,
"Won't be too long", he assured me,
But quick it was not, and the bone-headed clot
Took forty-five goes 'til he floored me.
And so I was dead, but my faithful old head
It never saw fit to desert me,
It still lingers on, that's the end of my song,
And now, please applaud, or you'll hurt me.