Layer in earth entrenched (3)
I believe the answer is:
hen
'layer' is the definition.
(I've seen this in other clues)
'in earth entrenched' is the wordplay.
'in' indicates the answer is hidden within the clue.
'HEN' is hidden in the letters of 'earth entrenched'.
(Other definitions for hen that I've seen before include "Coop resident" , "Domestic egg layer" , "Domestic fowl" , "Insufficient in amount" , "Source of eggs" .)