mandatory

Dictionary.com/mandatory:

"mandatory
\Man'da*to*ry\, a. [L. mandatorius.] Containing a command; preceptive; directory.

Source: Webster's Revised Unabridged Dictionary, � 1996, 1998 MICRA, Inc.

mandatory
adj : required by rule; 'in most schools physical education are compulsory'; 'attendance is mandatory'; 'required reading' [syn: compulsory, required] n : the recipient of a mandate [syn: mandatary]

Source: WordNet � 1.6, � 1997 Princeton University"