Observe thousand people in bed (7)
I believe the answer is:
comment
'observe' is the definition.
(commenting is a kind of observing)
'thousand people in bed' is the wordplay.
'thousand' becomes 'm' (Roman numeral for a thousand).
'people' becomes 'men' (men are people).
'in' means one lot of letters goes inside another.
'bed' becomes 'cot' (cot is a kind of bed).
'm'+'men'='mmen'
'mmen' going within 'cot' is 'COMMENT'.
(Other definitions for comment that I've seen before include "Leader writer's forte" , "offer opinion" , "observation" , "Nancy's version of how" , "Explanatory note" .)