Definition of bitter apple in English:

bitter apple

noun

another term for colocynth
‘The pulp is very bitter; hence the terms bitter apple, devil's apple, &c., by which it is popularly known.’
  • ‘Colocynth, or bitter apple, from India and Saharan Africa, was termed a "drastic" and "powerful" purge.’
  • ‘The bitter apple, Citrullus colocynthis, has a spongy pulp that when dried is the source of the glucosidal drug colocynth.’

Pronunciation

bitter apple

/ˈbidər ˈapəl/ /ˈbɪdər ˈæpəl/