Tolerating delay saying goodbye to island, that’s clear (6)
I believe the answer is:
patent
'clear' is the definition.
(synonyms)
'tolerating delay saying goodbye to island' is the wordplay.
'tolerating delay' becomes 'patient' (patience means tolerating delays).
'saying goodbye to' suggests deleting specific letters.
'island' becomes 'i' (geographical abbreviation).
'patient' with 'i' removed is 'PATENT'.
'that's' is the link.
(Other definitions for patent that I've seen before include "Blatant" , "This leather has a glossy varnished surface" , "The right to an invention is clear" , "Registration of an invention or trade name" , "Licence for invention; obvious" .)