late 14c., "a portion of something, a part" (sense preserved in phrase parcel of land, c. 1400), from Old French parcele "small piece, particle, parcel," from Vulgar Latin *particella, extended form (via diminutive suffix, but not necessarily implying smallness) of Latin particula "small part, little bit," itself a diminutive of pars (genitive partis) "a part, piece, fraction" (from PIE root *pere- (2) "to grant, allot").
Meaning "package" is first recorded 1640s, earlier "a quantity of goods in a package" (mid-15c.), from late 14c. sense of "an amount or quantity of anything." The expression part and parcel (early 15c.) also preserves the older sense; both words mean the same, the multiplicity is for emphasis.