Disloyal Toronto extremists accept explanation offered by American (10)
I believe the answer is:
treasonous
'disloyal' is the definition.
(similar in meaning)
'toronto extremists accept explanation offered by american' is the wordplay.
'extremists' says to hollow out the word (remove centre letters) (letters on the extreme ends of the word).
'accept' means one lot of letters goes inside another.
'explanation' becomes 'reason' (reason is a kind of explanation).
'offered by' says to put letters next to each other.
'american' becomes 'US' (United States).
'toronto' with its centre taken out is 'to'.
'to' placed around 'reason' is 'treasono'.
'treasono'+'us'='TREASONOUS'
(Other definitions for treasonous that I've seen before include "disloyal" , "subversive" , "Betraying one's country" , "Like Benedict Arnold, for some!" , "criminal" .)