First light? (3,6)
I believe the answer is:
one across
'first light?' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'first light?' is the wordplay.
'first' becomes 'one' (I've seen this in another clue).
'light?' becomes 'across' (I can't explain this - if you can you should give a lot more credence to this answer).
'one'+'across'='ONE ACROSS'
Can you help me to learn more?
(Other definitions for one across that I've seen before include "being absent from the puzzle" , "Usually the first clue (though not here!)" .)