Ship heading off - then a return to island? It shows reluctance to move (7)
I believe the answer is:
inertia
'reluctance to move' is the definition.
(I've seen this before)
'ship heading off then a return to' is the wordplay.
'ship' becomes 'liner' (liner is a kind of ship).
'heading off' means to remove the first letter.
'then' means one lot of letters go next to another.
'a return to' becomes 'tia' (I can't explain this - if you can you should believe this answer much more).
'liner' with its initial letter removed is 'iner'.
'iner'+'tia'='INERTIA'
'island? it shows' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for inertia that I've seen before include "Sort of reel" , "showing reluctance to move" , "Tendency to remain at rest or in steady motion" , "Feeling of slowness to act, as I retain" , "Listlessness" .)