Deranged Argonaut's source of bitterness? (9)
I believe the answer is:
angostura
'source of bitterness?' is the definition.
'angostura' can be an answer for 'source' (I have seen 'bitter source' mean 'angostura' so perhaps 'source' could also mean 'angostura'). I'm not sure about the 'of bitterness?' bit.
'deranged argonaut's' is the wordplay.
'deranged' indicates anagramming the letters.
'argonauts' anagrammed gives 'ANGOSTURA'.
Can you help me to learn more?
(Other definitions for angostura that I've seen before include "Bitter bark used as a flavouring" , "bitter substance" , "bitter source" , "Bitters for 13" , "special flavour" .)