Old Ethiopian gets half-cut in Gulf (5)
I believe the answer is:
abyss
'gulf' is the definition.
(an abyss is a gulf or chasm)
'old ethiopian gets half-cut' is the wordplay.
'old ethiopian' becomes 'Abyssinian' (Ethiopia was formerly known as Abyssinia).
'gets half-cut' suggests halving the letters.
'abyssinian' halved is 'ABYSS'.
'in' acts as a link.
(Other definitions for abyss that I've seen before include "Bottomless pit" , "deep depression" , "Deep hole, seems bottomless" , "Measureless chasm" , "Very deep gorge" .)