Crude Speedo bikini - small bottoms (3)
I believe the answer is:
oil
'crude' is the definition.
(crude oil)
'speedo bikini small bottoms' is the wordplay.
'bottoms' indicates one should take the final letters (I've seen 'bottom of' mean this).
The final letters of 'speedo bikini small' are 'OIL'.
(Other definitions for oil that I've seen before include "Slippery liquid" , "Liquid gold" , "Valuable viscous liquid" , "valuable commodity" , "eg Olive" .)