commercial motor oil additive, probably an initialism (acronym) of scientifically treated petroleum. As the street name of a type of psychedelic drug, attested from 1967.
stout
stove
stove-pipe
stow
stowaway
STP
strabismus
straddle
Stradivarius
strafe
straggle
)window.location='https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=byronic106@yahoo.com&lc=US&item_name=Donation+to +Help+Keep+Etymonline+Free+and+Open&no_note=0&cn=&curency_code=USD&bn=PP-DonationsBF:btn_donateCC_LG.gif:NonHosted'){kind=link}