Word of apology and love repeatedly added to extra note (4)
I believe the answer is:
oops
'word of apology' is the definition.
('oops' might be said as an apology)
'love repeatedly added to extra note' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'repeatedly' indicates the doubling of some letters.
'added to' says to put letters next to each other.
'extra note' becomes 'PS' (a PS or postscript in a letter).
'o' doubled is 'oo'.
'oo'+'ps'='OOPS'
'and' is the link.
(Other definitions for oops that I've seen before include "Exclamation recognising a mistake has been made" , "I've made a mistake!" , "Apologetic exclamation" , "Exclamation on making obvious mistake" , "Clumsy me!" .)