Some err badly and show regret (7)
I believe the answer is:
remorse
'show regret' is the definition.
'remorse' can be an answer for 'regret' (remorse is a feeling of regret). I'm unsure of the 'show' bit.
'some err badly' is the wordplay.
'badly' indicates an anagram.
'some'+'err'='someerr'
'someerr' anagrammed gives 'REMORSE'.
'and' is the link.
Can you help me to learn more?
(Other definitions for remorse that I've seen before include "Ruefulness" , "compassion" , "Regret for wrong" , "display of conscience" , "Self-reproach" .)