Prop (up) (5)
'prop up' is the definition.
(bolstering is a kind of propping up)
This is the entire clue.
(Other definitions for bolster that I've seen before include "Lobster (anag.)" , "Chisel - long cushion" , "Extended pillow" , "support for head after retiring" , "Strengthen - long pillow" .)
'prop up' is the definition.
(I know that prop up can be written as shore)
This is all the clue.
(Other definitions for shore that I've seen before include "Land beside sea, lake" , "Prop; coastline" , "Coast" , "Land by water" , "support being only temporary?" .)