From mid-14c. with senses "lose one's footing," "slide out of place," "fall into error or fault." Sense of "pass unguarded or untaken" is from mid-15c. That of "slide, glide" is from 1520s. Transitive sense from 1510s; meaning "insert surreptitiously" is from 1680s. Related: Slipped; slipping. To slip up "make a mistake" is from 1855; to slip through the net "evade detection" is from 1902. To let (something) slip originally (1520s) was a reference to hounds on a leash; figurative use "allow to escape through carelessness" is from 1540s.
c. 1400, loupen, "to draw (a leash through a ring)," from loop (n.). Sense of "form into a loop or loops" (transitive) is from 1832; transitive meaning "form (something) into loops" is from 1856. Related: Looped (1934 in the slang sense "drunk"); looping. Loop the loop (1900) originally was in reference to roller-coasters at amusement parks.
"Loop-the-Loop" is the name of a new entertainment which goes further in the way of tempting Providence than anything yet invented. The "Loop" is an immense circle of track in the air. A car on a mimic railway shoots down a very steep incline, and is impelled around the inner side of this loop. ... The authorities at Coney Island are said to have prohibited "looping-the-loop" because women break their corset strings in their efforts to catch their breath as they sweep down the incline, and moreover, a young man is reported to have ruptured a blood vessel in his liver. ["Philadelphia Medical Journal," Aug. 10, 1901]