Instrument with a long needle (7)

I believe the answer is:

althorn

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'instrument' is the definition.
(I've seen this before)

'with a long needle' is the wordplay.
'with' is a charade indicator (letters next to each other).
'long' becomes 'l'.
'needle' becomes 'thorn' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'l' is 'al'.
'al'+'thorn'='ALTHORN'

Can you help me to learn more?

(Other definitions for althorn that I've seen before include "one of the brass" , "musical instrument" .)

I've seen this clue in The Hindu.

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