Valid a. : Strong; powerful; efficient.

Valid a. : 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.

Valid a. : 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.

Example:
What are Valid reasons for university classes to be cancelled?

Taxonomy
premises, conclusion, Socrates, interpretation, logical truth, deductive validity, valid argument, false conclusion, true premises, logic, truth, logical form, deduction, free encyclopedia, Logical truths, true conclusion, false premises, argument form.

Defination from the web:
valid if and only if the truth of its premises entails the truth of its conclusion. ... The corresponding conditional of a valid argument is a logical truth and the negation of its corresponding conditional is a contradiction. ...