'Disciplinary' (relating to discipline or punishment) is formed from 'discipline' by dropping the final 'e' and adding '-ary'. The correct spelling maintains 'dis-CIP-line' before the suffix. Options A (Discipilanry), B (Discipilnary), and D (Discplanry) incorrectly swap 'i' and 'a' or drop the 'e' and change the vowel order.