One leaving airman in bed (4)
I believe the answer is:
plot
'bed' is the definition.
(I've seen this before)
'one leaving airman' is the wordplay.
'one' becomes 'i' (Roman numeral).
'leaving' indicates named letters should be taken away.
'airman' becomes 'pilot' (pilot is a kind of airman).
'pilot' with 'i' taken out is 'PLOT'.
'in' acts as a link.
(Other definitions for plot that I've seen before include "Scheme, story and piece of ground" , "garden area" , "Small area of ground" , "Area of ground; storyline" , "Scheme; graph" .)