One figures out that it's central (3)
I believe the answer is:
mid
'that it's central' is the definition.
(thesaurus)
'one figures out' is the wordplay.
'one' becomes 'I' (Roman numeral).
'figures' becomes 'md' (I can't justify this - if you can you should give a lot more credence to this answer).
'out' indicates putting letters inside.
'i' going within 'md' is 'MID'.
Can you help me to learn more?
(Other definitions for mid that I've seen before include "Of the central part" , "Denote the centre point" , "Dim sort of prefix" , "Prefix meaning centre" .)