Without it, the speaker would dry up (6)
I believe the answer is:
saliva
'dry up' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'without it the speaker would' is the wordplay.
I cannot quite understand how this works, but
'it' could be 'sa' (old-fashioned abbreviation for sex appeal) and 'sa' is present in the answer.
'speaker' could be 'i' ('I' refers to the person saying it) and 'i' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for saliva that I've seen before include "Mouth moisture, spittle" , "Oral secretion" , "Liquid that moistens the mouth" , "Clear liquid secreted into the mouth" , "Mouth secretion" .)