The central part is in semi-darkness (3)
I believe the answer is:
mid
'the central' is the definition.
(thesaurus)
'in semi-darkness' is the wordplay.
'in' indicates a hidden word.
'MID' is hidden within 'semi darkness'.
'part is' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for mid that I've seen before include "Denote the centre point" , "Of the central part" , "Dim sort of prefix" , "Prefix meaning centre" .)