Spear in butcher's no good (5)
I believe the answer is:
lance
'spear' is the definition.
(I know that spear can be written as lance)
'butcher's no good' is the wordplay.
'butcher's' becomes 'glance' (butcher's hook is Cockney rhyming slang for look).
'no' indicates named letters should be taken away.
'good' becomes 'g' (abbreviation).
'glance' with 'g' taken away is 'LANCE'.
'in' acts as a link.
(Other definitions for lance that I've seen before include "Horseman's long weapon" , "Weapon of knights of old" , "surgical instrument" , "Knightly weapon" , "Shafted weapon used on horseback" .)