Fortify large space next to Sussex town (8)
I believe the answer is:
embattle
'fortify' is the definition.
(I know this)
'large space next to sussex town' is the wordplay.
'large space' becomes 'em' (in typography, a space as wide as a letter 'm'. I am not sure about the 'large' bit.).
'next to' says to put letters next to each other.
'sussex town' becomes 'battle' (I've seen this before).
'em'+'battle'='EMBATTLE'
Can you help me to learn more?
(Other definitions for embattle that I've seen before include "Fortify" , "Prepare for conflict" , "Beset with attacks" , "add strength" , "Make ready to fight; belt mate (anagram)" .)