well-grounded on principles or evidence; able to withstand criticism or objection, as an argument; sound; in testing, describes a test that measures what it purports to measure.

relevant In such cases the neighbour principle ought to apply unless there is some justification or valid explanation for its exclusion. validity (n)

Well grounded on principles or evidence. Able to stand criticism or objection; sound, meaningful.

a) Well-grounded or justifiable; being at once relevant and meaningful, e.g., a valid theory; b) Logically correct. (W)

Accurate, precise, reliable, authorized and relevant.

(1) Sound. (2) Well grounded on principles of evidence. (3) Able to withstand criticism or objection.