Ship heading off with Spanish aunt showing a tendency to do nothing (7)
I believe the answer is:
inertia
'a tendency to do nothing' is the definition.
(I've seen this before)
'ship heading off with spanish aunt' is the wordplay.
'ship' becomes 'liner' (liner is a kind of ship).
'heading off' means to remove the first letter.
'with' says to put letters next to each other.
'spanish aunt' becomes 'tia' ('aunt' in Spanish).
'liner' with its first letter removed is 'iner'.
'iner'+'tia'='INERTIA'
'showing' is the link.
(Other definitions for inertia that I've seen before include "Slowness to act, lassitude" , "Tendency to do nothing or to remain unchanged" , "inclination not to budge" , "Stillness" , "Disposition to do nothing" .)