Everyman finally monopolizes chaise longue, that's clear (1,3)
I believe the answer is:
i see
'that's clear' is the definition.
(I've seen this in another clue)
'everyman finally monopolizes chaise longue' is the wordplay.
'everyman' becomes 'i' (where 'Everyman' is the setter of the crossword).
'finally' indicates one should take the final letters.
The final letters of 'monopolizes chaise longue' are 'see'.
'i'+'see'='I SEE'
(Other definitions for i see that I've seen before include "Got it now!" , "So that's the way the cookie crumbles!" , "Expression of dawning comprehension" .)