Love letter initially in bold (7)
I believe the answer is:
darling
'love' is the definition.
(both are terms of endearment)
'letter initially in bold' is the wordplay.
'initially' indicates taking the first letters.
'in' indicates putting letters inside.
'bold' becomes 'daring' (I've seen this before).
The initial letter of 'letter' is 'l'.
'l' going inside 'daring' is 'DARLING'.
(Other definitions for darling that I've seen before include "Grace -, nineteenth century wreck heroine of lighthouse" , "Term of endearment" , "Beloved" , "Victorian heroine" , "lover" .)