Info on an alien animal (5)
I believe the answer is:
genet
'animal' is the definition.
(thesaurus)
'info on an alien' is the wordplay.
'info' becomes 'gen' (informal term for information).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'an alien' becomes 'ET' (extra terrestrial).
'gen'+'et'='GENET'
(Other definitions for genet that I've seen before include "Agile, cat-like animal" , "(Fur from) cat - French writer" , "French playwright" , "furry beast" , "Catlike mammal; Jean --, French author" .)