Pretends, when one allows to board (4,2)
I believe the answer is:
lets on
'pretends' is the definition.
(I've seen this in another clue)
'when one allows to board' is the wordplay.
I cannot quite understand how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is found in the answer.
'allows' could be 'lets' ('let' can be a synonym of 'allow') and 'lets' is found within the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for lets on that I've seen before include "Pretends or allows to come aboard" , "Discloses (secret) information" .)