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Lookups spiked on June 14, 2013.
A happy little song got dragged into court.
A production company that is making a film about "Happy Birthday" filed a suit against the copyright holders of that song, claiming that there is no current and valid copyright and it resides in the public domain.
This particular use of valid ("having legal efficacy or force") is also the oldest: the word was used exclusively in legal settings for the first 75 years of its life.
Valid originates in the Latin verb valere, meaning "to be strong or powerful," and entered English in the 16th century. The meaning of valid broadened in the 17th century to "justifiable" and then "effective," but the original legal use is still commonly heard in phrases like "a valid contract" and "a valid copyright."