Regarding charge? One’s postponed endlessly (5)
I believe the answer is:
ionic
'regarding charge?' is the definition.
'one's postponed endlessly' is the wordplay.
'one' becomes 'i' (Roman numeral).
'postponed' becomes 'onice' (I've seen this before).
'endlessly' means to remove the last letter.
'onice' with its final letter removed is 'onic'.
'i'+'onic'='IONIC'
(Other definitions for ionic that I've seen before include "ancient Greek dialect" , "Architectural order" , "Greek architectural style" , "Greek school" , "Style of Greek column used for the British Museum and the US Capitol" .)