1 general:: necessary, essential
transnet.ir
2 Law:: necessary; obligatory; must (Is it a must?( ● incumbent; essential; needed; required; compulsory; indispensable; mandatory; requisite; de rigueur : prescribed or required by fashion, etiquette , or custom : proper (instructions as to when and where a tuxedo is de rigueur( sine qua non (Lat) : something absolutely indispensable or essential (reliability is a sine qua non for success(
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