Welsh are about on island, more than a few. It's tiresome (9)
I believe the answer is:
wearisome
'tiresome' is the definition.
(synonyms)
'welsh are about on island more than a few' is the wordplay.
'welsh' becomes 'W'.
'about' indicates an anagram.
'on island' becomes 'some' (I can't justify this - if you can you should believe this answer much more).
'more than' means one lot of letters go next to another.
'a few' becomes 'i'.
'are' anagrammed gives 'ear'.
'some' after 'i' is 'isome'.
'w'+'ear'+'isome'='WEARISOME'
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for wearisome that I've seen before include "Boring" , "pestilential" , "Trying" , "Tedious, tiring" , "Vexatious" .)