Blade for piercing tip of darning needle (4)

I believe the answer is:

dirk

I'm a little stuck... Click here to teach me more about this clue!

'blade for piercing' is the definition.
I can't judge whether this defines the answer.

'tip of darning needle' is the wordplay.
'tip of' indicates taking the first letters.
'needle' becomes 'irk' (I've seen this in another clue).
The initial letter of 'darning' is 'd'.
'd'+'irk'='DIRK'

Can you help me to learn more?

(Other definitions for dirk that I've seen before include "Dagger with a long straight blade" , "Dagger (belonging to Bogarde?)" , "Scots dagger" , "Highland dagger" , "Duncan's killer?" .)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.