Large ears reshaped in surgical beam (5)
I believe the answer is:
laser
'surgical beam' is the definition.
(as in laser surgery)
'large ears reshaped in' is the wordplay.
'large' becomes 'l' ().
'reshaped' indicates anagramming the letters.
'in' indicates putting letters inside.
'ears' is an anagram of 'aser'.
'l' put inside 'aser' is 'LASER'.
(Other definitions for laser that I've seen before include "Device that generates an intense beam of light" , "Surgical device" , "Device yielding powerful beam" , "Light amplification by stimulated emission of radiation" , "scientific device" .)