It suggests there's something bad about a good start (4)
I believe the answer is:
sign
'it suggests' is the definition.
The definition suggests a singular noun which matches the answer.
'something bad about a good start' is the wordplay.
'something bad' becomes 'sin' (something morally bad).
'about' means one lot of letters goes inside another.
'start' suggests taking the first letters.
The first letter of 'good' is 'g'.
'sin' going around 'g' is 'SIGN'.
'there's' acts as a link.
Can you help me to learn more?
(Other definitions for sign that I've seen before include "Public notice; gesture" , "Authorise with a name" , "Put one's name to a document" , "Engage by written agreement" , "Manifestation" .)