“Cay” and “Quay” said to be essential elements for searching (8)
I believe the answer is:
keywords
'be essential elements for searching' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'cay and quay said' is the wordplay.
'cay' becomes 'words' (I can't explain this - if you can you should give a lot more credence to this answer).
'and' says to put letters next to each other.
'said' shows a homophone (sound like).
'quay' is a homophone of 'key'.
'words' put after 'key' is 'KEYWORDS'.
'to' acts as a link.
Can you help me to learn more?
(Another definition for keywords that I've seen is " vital letter-sets".)