1560s, probably an alteration of stridlen, frequentative of striden (see stride). U.S. colloquial sense of "take up an equivocal position, appear to favor both sides" is attested from 1838. Related: Straddled; straddling. The noun is first recorded 1610s.
A powerful hallucinogen: a strictly contemporary folk drug, called STP by its Haight-Ashbury discoverers
[1960s+ Narcotics; fr Serenity Tranquility Peace, named in imitation of the oil additive STP2]