Round container holds tablet and a lot of water (5)
I believe the answer is:
ocean
'a lot of water' is the definition.
(oceans are made up of water)
'round container holds tablet and' is the wordplay.
'round' is an insertion indicator.
'container holds' becomes 'oca' (I can't justify this - if you can you should believe this answer much more).
'tablet' becomes 'e' (E can mean ecstasy or an ecstasy tablet).
'and' becomes 'n' (common abbreviation for 'and').
'oca' placed around 'e' is 'ocea'.
'ocea'+'n'='OCEAN'
Can you help me to learn more?
(Other definitions for ocean that I've seen before include "A lot of water!" , "Indian or Arctic, say" , "Vast sea" , "Indian perhaps" , "Extensive sea area" .)