Server dropping one drink (5)
I believe the answer is:
water
'drink' is the definition.
(I know that water is a type of drink)
'server dropping one' is the wordplay.
'server' becomes 'waiter' (synonyms).
'dropping' is a deletion indicator.
'one' becomes 'I' (Roman numeral).
'waiter' with 'i' taken out is 'WATER'.
(Other definitions for water that I've seen before include "something damp" , "Colourless, odourless and tasteless liquid" , "Quality of diamonds" , "Basic liquid" , "Commonplace drink" .)