Ray internalises Republican motto (6)
I believe the answer is:
mantra
'motto' is the definition.
(a mantra is a repeated word or motto)
'ray internalises republican' is the wordplay.
I cannot really understand how this works, but
'republican' could be 'r' (abbreviation) and 'r' is found in the answer.
'ray' could be 'manta' (manta is a kind of ray) and 'manta' is present in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mantra that I've seen before include "Incantation, Hindu psalm" , "Phrase repeated as aid to meditation in Buddhism" , "Commonly repeated word or phrase, with religious connotation perhaps" , "Repetitive sacred utterance" , "Sound repeated as an aid to meditation" .)