Adult in bed with one animal (5)
I believe the answer is:
coati
'animal' is the definition.
(mammal of Central and South America)
'adult in bed with one' is the wordplay.
'adult' becomes 'a' (abbreviation).
'in' indicates putting letters inside.
'bed' becomes 'cot' (cot is a type of bed).
'with' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'a' placed into 'cot' is 'coat'.
'coat'+'i'='COATI'
(Other definitions for coati that I've seen before include "omnivorous mammal" , "S. and Central American raccoon-like animal" , "Furry animal" , "Raccoon-like animal of Central and S. America" , "carnivore from South America" .)