"seed of an apple," 1797, shortened form of pipin "seed of a fleshy fruit" (early 14c.), from Old French pepin (13c.), probably from a root *pipp-, expressing smallness (cf. Italian pippolo, Spanish pepita "seed, kernel").
"disease of birds," late 14c., probably from Middle Dutch pippe "mucus," from West Germanic *pipit (cf. East Frisian pip, Middle High German pfipfiz, German Pips), an early borrowing from Vulgar Latin *pippita, unexplained alteration of Latin pituita "phlegm" (see pituitary).
"spot on a playing card, etc." c.1600, peep, of unknown origin. Because of the original form, it is not considered as connected to pip (n.1). Related: Pips.
A minor skin lesion, esp of teenagers: whiteheads, blackheads, goopheads, goobers, pips, acne trenches (1676+)
: a pipperoo flick
[fr pippin, a prized kind of apple; the shift was probably fr peach as one kind of excellent fruit to pippin as another]