Eccentric loner intended heartless registration (9)
I believe the answer is:
enrolment
'registration' is the definition.
(eg enrolling at a university)
'eccentric loner intended heartless' is the wordplay.
'eccentric' indicates an anagram.
'intended' becomes 'meant' (to mean something is to intend it).
'heartless' says to hollow out the word (remove centre letters).
'meant' with its centre taken out is 'ment'.
'loner' anagrammed gives 'enrol'.
'enrol'+'ment'='ENROLMENT'
(Other definitions for enrolment that I've seen before include "signing up" , "matriculation" , "Joining" , "Registration" , "Act of entering on a list of members" .)