Guard, engineer, nurse, butcher (6)
I believe the answer is:
ensure
'guard' is the definition.
(I've seen this in another clue)
'engineer nurse butcher' is the wordplay.
'engineer' becomes 'e' (this might be a standard abbreviation of which I'm unaware).
'butcher' indicates an anagram (I've seen 'butchered' mean this (I've seen this in other clues)).
'nurse' anagrammed gives 'nsure'.
'e'+'nsure'='ENSURE'
Can you help me to learn more?
(Other definitions for ensure that I've seen before include "warrant" , "Make certain, clinch" , "Make certain, confirm" , "Make certain for the future" , "Make certain or safe" .)