Of a person: worth blackmailing; susceptible to blackmail. Of behaviour, information, etc.: suitable for being used as a basis for blackmail; damaging or incriminating.
Origin
Early 20th century. From blackmail + -able.
Definition of blackmailable in US English:
blackmailable
adjectiveˈblakmeɪləbl
Of a person: worth blackmailing; susceptible to blackmail. Of behaviour, information, etc.: suitable for being used as a basis for blackmail; damaging or incriminating.