Pruning tool sick husband kept in reserve (8)

I believe the answer is:

billhook

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'pruning tool' is the definition.
'billhook' can be an answer for 'tool' (billhook is a kind of tool). I'm not sure about the 'pruning' bit.

'sick husband kept in reserve' is the wordplay.
'sick' becomes 'ill' (synonyms).
'husband' becomes 'h'.
'kept in' means one lot of letters goes inside another.
'reserve' becomes 'book' (to book something is to reserve it).
'ill'+'h'='illh'
'illh' put inside 'book' is 'BILLHOOK'.

Can you help me to learn more?

(Other definitions for billhook that I've seen before include "Cutter" , "Tree-pruning tool" , "I'll prune" , "Mini-scythe" .)

I've seen this clue in The Independent.

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