A number eating seconds and wanting a drink (7)
I believe the answer is:
thirsty
'wanting a drink' is the definition.
(I've seen this before)
'a number eating seconds' is the wordplay.
'a number' becomes 'thirty' (thirty is a kind of number**).
'eating' means one lot of letters goes inside another.
'seconds' becomes 's'.
'thirty' placed around 's' is 'THIRSTY'.
'and' acts as a link.
(Other definitions for thirsty that I've seen before include "Gasping" , "Dry" , "Parched" , "Hungry" , "Keen" .)