Nominally speaking, it's capitalised at the start (7)
I believe the answer is:
initial
'the start' is the definition.
(I have seen 'Start of name' mean 'initial' so perhaps 'start' could also mean 'initial')
'nominally speaking it's capitalised at' is the wordplay.
I cannot quite understand how this works, but
'at' could be 'in' and 'in' is found within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for initial that I've seen before include "First letter (of a word)" , "shortened version of my name" , "Sign" , "Letter - opening" , "Endorse" .)