Capable of being disciplined; responsive to training, instruction, or rules.
From discipline + -able (capable of), following the productive pattern in English of adding -able to verbs to create adjectives meaning 'capable of being' the verb's action.
The '-able' suffix is one of English's greatest productivity tools—almost any verb can accept it (readable, drinkable, fixable)—making 'disciplinable' a naturally formed but rarely needed adjective!
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