550 leaving also pipe up "farewell!" (6-3)
I believe the answer is:
toodle-pip
'farewell' is the definition.
(I know that farewell can be written as toodle-pip)
'550 leaving also pipe up' is the wordplay.
I cannot quite understand how this works, but
'also' could be 'too' (synonyms) and 'too' is located in the answer.
an anagram of 'pipe' is 'epip' which is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for toodle-pip that I've seen before include "Farewell remark - dipole top (anag)" , "Farewell (informal)" , "so long" , "Goodbye (dated)" , "Take care" .)