Aware of pontoon syndicate (4)
I believe the answer is:
onto
'aware of' is the definition.
(if you're onto someone you know what they're up to)
'pontoon syndicate' is the wordplay.
'ONTO' is hidden within the letters.
But, I am unsure how this is indicated.
Can you help me to learn more?
(Other definitions for onto that I've seen before include "To a position on (something)" , "Conscious of" , "forward, with a destination" , "(Moving) aboard" , "In contact with - aware of" .)