Priest cuts shin up with large knife (7)
I believe the answer is:
scalpel
'knife' is the definition.
(scalpel is a kind of knife)
'priest cuts shin up with large' is the wordplay.
'priest' becomes 'p' (ecclesiastical abbreviation).
'cuts' indicates putting letters inside (some letters cut their way into other letters).
'shin up' becomes 'scale' (both can mean to climb).
'with' says to put letters next to each other.
'large' becomes 'L' (eg in clothes sizes).
'p' placed within 'scale' is 'scalpe'.
'scalpe'+'l'='SCALPEL'
(Other definitions for scalpel that I've seen before include "Sharp blade" , "Surgical implement" , "Small surgical knife" , "One making cuts in hospital" , "Surgical blade" .)