The lot of the viewer (5)
I believe the answer is:
sight
This clue is a double definition.
'the lot' is the first definition.
(sight can informally mean a lot of something)
'of the viewer' is the second definition.
(a viewer uses sight)
(Other definitions for sight that I've seen before include "Could be a jolly" , "Bodily faculty" , "Place worth visiting" , "Spot - eyesore" , "Show" .)