Unending regalia for an organ (5)
I believe the answer is:
liver
'organ' is the definition.
(I know that liver is a type of internal organ)
'unending regalia for an' is the wordplay.
I cannot quite see how this works, but
'an' could be 'i' (Roman numeral for one) and 'i' is found in the answer.
The remaining letters 'lver' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for liver that I've seen before include "Glandular organ in the abdomen" , "Bodily organ" , "Glandular organ of the stomach" , "Viler (anag.)" , "Detoxifying organ" .)