Old car initially on reef - a submerged reef (7)
I believe the answer is:
bombora
'submerged reef' is the definition.
'bombora' can be an answer for 'reef' (I've seen this before). I'm unsure of the 'submerged' bit.
'old car initially on reef a' is the wordplay.
'old car' becomes 'bomb' (I can't justify this - if you can you should believe this answer much more).
'initially' says to take the initial letters.
The first letters of 'on reef' is 'or'.
'bomb'+'or'+'a'='BOMBORA'
Can you help me to learn more?
(Another definition for bombora that I've seen is " submerged reef in Australia".)