On the Thames, it's of unusual note (4)
I believe the answer is:
eton
'on the thames it's' is the definition.
I can't judge whether this definition defines the answer.
'unusual note' is the wordplay.
'unusual' is an anagram indicator.
'note' anagrammed gives 'ETON'.
'of' is the link.
Can you help me to learn more?
(Other definitions for eton that I've seen before include "School near Slough" , "English college of note" , "old school" , "College in Berkshire" , "Famous English public school" .)