Attempt to admit regrets the speaker makes repellent (8)
I believe the answer is:
gruesome
'repellent' is the definition.
(thesaurus)
'attempt to admit regrets the speaker' is the wordplay.
'attempt' becomes 'go' (go is a kind of attempt).
'to admit' means one lot of letters goes inside another.
'regrets' becomes 'rues' ('rue' can be a synonym of 'regret').
'the speaker' becomes 'me'.
'go' enclosing 'rues' is 'grueso'.
'grueso'+'me'='GRUESOME'
'makes' is the link.
(Other definitions for gruesome that I've seen before include "Repulsive, horrific" , "Go, resume being revolting or gruesome" , "'Grisly, macabre (8)'" , "'Ghastly, grisly (8)'" , "Repulsive, horrid" .)