valid

Etymology

Borrowed from Middle French valide (“healthy, sound, in good order”), from Latin validus, from valeō (“I am strong, I am healthy, I am worth”) + -idus, from Proto-Indo-European *h₂welh₁- (“be strong”).

adj

1. Well grounded or justifiable, pertinent.
   I will believe him as soon as he offers a valid answer.
   Few concepts are as emotionally charged as that of race. The word conjures up a mixture of associations—culture, ethnicity, genetics, subjugation, exclusion and persecution. But is the tragic history of efforts to define groups of people by race really a matter of the misuse of science, the abuse of a valid biological concept? 2012 March-April, Jan Sapp, “Race Finished”, in American Scientist, volume 100, number 2, page 164
2. Acceptable, proper or correct; in accordance with the rules.
   A valid format for the date is DD/MM/YY.
   Do not drive without a valid license.
3. Related to the current topic, or presented within context, relevant.
4. (logic) Of a formula or system: such that it evaluates to true regardless of the input values.
5. (logic) Of an argument: whose conclusion is always true whenever its premises are true.
   An argument is valid if and only if the set consisting of both (1) all of its premises and (2) the contradictory of its conclusion is inconsistent.
6. (Christianity, theology) Genuine - as distinguished from efficient or regular - sacrament.