...a number wanting a drink without speaking first (6)
I believe the answer is:
thirty
'a number' is the definition.
(thirty is a kind of number)
'wanting a drink without speaking first' is the wordplay.
'wanting a drink' becomes 'thirsty' (I've seen this in another clue).
'without' suggests deleting specific letters.
'speaking first' becomes 's' (1st letter of 'speaking').
'thirsty' with 's' taken away is 'THIRTY'.
(Other definitions for thirty that I've seen before include "Sum of first four perfect squares" , "Number of pieces of silver paid to Judas" , "The number of silver coins for betrayal" , "Both RU teams" , "Roman number XXX" .)