valid

valid
val‧id AC /ˈvæləd, ˈvælɪd/ adjective1. a valid ticket, document, or agreement is legally or officially acceptable
   OPP  invalid:
    a valid credit card
    Your return ticket is valid for three months.
2. valid reason/argument/criticism etc a reason, argument etc that is based on what is reasonable or sensible:
    Police officers must have a valid reason for stopping motorists.
3. a valid password, ID etc is one that will be accepted by a computer system
   OPP  invalid
—validity /vəˈlɪdəti, vəˈlɪdɪti/ noun [uncountable]:
    I would question the validity of that statement.
     

COLLOCATIONS

(for Meaning 2)

■ nouns
   ▪ point I think that's a valid point.
   ▪ reason I had a perfectly valid reason for being there.
   ▪ argument None of these arguments are valid.
   ▪ criticism If the criticism is valid, you should make the appropriate changes.
   ▪ excuse You must have a valid excuse for any absence.
■ adverbs
   ▪ equally valid Each of these ways of looking at things is equally valid.
   ▪ perfectly valid It's a perfectly valid question.
   ▪ statistically/scientifically valid (=based on correct numbers or good research) The drug trials were scientifically valid.