Shield of wood old so kept in Greek island (8)
I believe the answer is:
creosote
'shield of wood' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'old so kept in greek island' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'kept in' is an insertion indicator.
'greek island' becomes 'crete' (I've seen this before).
'o'+'so'='oso'
'oso' inserted into 'crete' is 'CREOSOTE'.
Can you help me to learn more?
(Other definitions for creosote that I've seen before include "Preservative liquid obtained from coal tar" , "Oily excretion" , "Dark oily liquid, preservative for wood" , "Oily liquid preservative -- eco-store (anag)" , "Oily, smelly wood preservative" .)