Middle (4)
'middle' is the definition.
(I know that middle can be written as centre)
This is all the clue.
(Other definitions for centre that I've seen before include "Point equidistant from all other points" , "Nucleus" , "'Things fall apart; the ... cannot hold'/Yeats" , "Pair of facing pages in the middle of a magazine" , "Midpoint" .)
'middle' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for central that I've seen before include "Middle; crucial" , "like this answer" , "Focal" , "Key" , "Near the middle" .)
'middle' is the definition.
(synonyms)
This is all the clue.
(Other definitions for waist that I've seen before include "Part of the trunk" , "part of frame" , "Between ribs and hips" , "Narrow part of body" , "Spare tyre location?" .)
'middle' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for midst that I've seen before include "In the middle of (archaic or literary)" , "Central part" , "Where one is surrounded by other things" , "Among, amid" , "Centre" .)
'middle' is the definition.
(core can mean the centre of something)
This is all the clue.
(Other definitions for core that I've seen before include "Inmost part" , "Central zone" , "Essence" , "The centre of an object" , "The centre part, as of an apple" .)