Serious wound admitted to A & E (5)
I believe the answer is:
acute
'serious' is the definition.
(thesaurus)
'wound admitted to a e' is the wordplay.
'wound' becomes 'cut' (cut is a kind of wound).
'admitted to' indicates putting letters inside.
'a'+'e'='ae'
'cut' going inside 'ae' is 'ACUTE'.
(Other definitions for acute that I've seen before include "Extremely sharp or intense" , "not seen in cafe here!" , "Penetrating; accent" , "Sharp or crucial" , "(Of an angle) less than 90 degrees" .)