Scottish side observed to absorb pressure when retreating (5)
I believe the answer is:
neeps
'scottish side' is the definition.
(Scottish term for turnips, a side in a meal)
'observed to absorb pressure when retreating' is the wordplay.
'observed' becomes 'seen' ('seen' can be a synonym of 'observed').
'to absorb' means one lot of letters goes inside another.
'pressure' becomes 'p' (abbreviation).
'when retreating' says the letters should be written in reverse.
'seen' placed around 'p' is 'speen'.
'speen' in reverse letter order is 'NEEPS'.
(Other definitions for neeps that I've seen before include "Scottish roots" , "Scottish turnips" , "Root vegetables" , "Scots turnips" .)