Reminder from lunatic over in US... (8)
I believe the answer is:
souvenir
'reminder' is the definition.
(I've seen this before)
'lunatic over in us' is the wordplay.
'lunatic' indicates an anagram.
'over'+'in'+'us'='overinus'
'overinus' anagrammed gives 'SOUVENIR'.
'from' acts as a link.
(Other definitions for souvenir that I've seen before include "Reminder of past events" , "Reminder of holiday" , "Keepsake, memento" , "remember seeing this?" , "something worth keeping" .)