Valid, a.
Etymology: [F. valide, F. validus strong, from valere to be strong. See Valiant.]
1. Strong; powerful; efficient. [Obs.] "Perhaps more valid arms . . . may serve to better us." Milton.
2. Having sufficient strength or force; founded in truth; capable of being justified, defended, or supported; not weak or defective; sound; good; efficacious; as, a valid argument; a valid objection. An answer that is open to no valid exception. I. Taylor.
3. (Law)
Having legal strength or force; executed with the proper formalities; incapable of being rightfully overthrown or set aside; as, a valid deed; a valid covenant; a valid instrument of any kind; a valid claim or title; a valid marriage.
1 more senses
Syn. -- Prevalent; available; efficacious; just; good; weighty; sufficient; sound; well-grounded.
Shades of meaning
Fernald lists valid only as an antonym, under vain.
He lists it without comment; the entries above explain its neighbors.