word-forming element meaning "bulk, mass," used from 19c., especially in medical use, "tumor," from Latinized form of Greek ogkos (pronounced "onkos") "bulk, size, mass, weight, swelling," in Modern Greek "tumor," a word of uncertain origin.
word-forming element meaning "toward or on the right-hand side," from combining form of Latin dexter (from PIE root *deks- "right, opposite of left; south").
spelling conventional in 15c.-17c. English to add emphasis to borrowed French nouns ending in stressed -on; also used to represent Italian -one, Spanish -ón; all from Latin -onem. Compare shalloon (1670s) for French chalon, a kind of material used for linings. The ending is used occasionally to form words in English, such as spittoon, quadroon, and some older ones no longer with us, such as shabberoon "disreputable person" (c. 1700).