valid
1 acceptable, binding, cogent, conclusive, convincing, efficacious, efficient, good, just, logical, powerful, sensible, sound, substantial, telling, weighty, well-founded, well-grounded
2 authentic, bona fide, genuine, in force, lawful, legal, legally binding, legitimate, official, signed and sealed
Antonyms
1 baseless, bogus, fallacious, false, illogical, sham, spurious, unacceptable, unfounded, unrealistic, unrecognized, untrue, weak
2 illegal, inoperative, invalid, unlawful, unofficial