Sound asleep, embracing Kelvin, having left dive? (7)
I believe the answer is:
snorkel
'dive?' is the definition.
(I know that snorkel is a type of dive)
'sound asleep embracing kelvin having left' is the wordplay.
'sound asleep' becomes 'snore' (sound made by a sleeping person).
'embracing' means one lot of letters goes inside another.
'kelvin' becomes 'K' (abbreviation for the unit of temperature).
'having' says to put letters next to each other.
'left' becomes 'l' (common abbreviation).
'snore' enclosing 'k' is 'snorke'.
'snorke'+'l'='SNORKEL'
(Other definitions for snorkel that I've seen before include "Bent tube for a swimmer's mouth" , "Surface swimmer's breathing aid" , "diving equipment?" , "Breathing pipe for swimmers" , "Diver's air-tube" .)