Jumble sale in extraterrestrials? (6)
I believe the answer is:
aliens
'extraterrestrials?' is the definition.
('alien' can be a synonym of 'extraterrestrial')
'jumble sale in' is the wordplay.
'jumble' indicates an anagram.
'sale'+'in'='salein'
'salein' anagrammed gives 'ALIENS'.
(Other definitions for aliens that I've seen before include "Creatures from another planet" , "'Little green men'?" , "Life-forms assumed to exist beyond Earth" , "Foreigners or creatures from outer space" , "Outsiders" .)