-on gen.pl. ending (3O), in aldaron, aranion, elenion, Eldaron, #esseron, Ingweron, Istarion, Númevalion, Quendion, Silmarillion, Sindaron, tasarion (see Nan-Tasarion), Valion, wenderon, yénion. Normally the ending -on is added to the nominative plural, whether it ends in -i or -r, but some nouns in -ë that would have nominative plurals in -i seem to prefer the ending -ron in the genitive (hence #esseron as the gen. pl. of essë "name", though the nominative pl. is attested as essi and we might have expected the gen. pl. *ession; similarly wenderon, Ingweron).
Quenya
-on
-on
-on
name
-on
suffix. augmentative, great
-ion
suffix. -son, masculine patronymic
The usual patronymic for “son of” in Quenya, suffixal form of Q. yondo “son” (PE17/170, 190). Tolkien occasionally mentioned variants like -on or -yon, but in practice only -ion appears in actual names.
Conceptual Development: This patronymic dates all the way back to Qenya Lexicon of the 1910s (QL/106) and was regularly mentioned in documents throughout the years such as the Early Qenya Grammar and English-Qenya Dictionary of the 1920s (PE14/45, 75; PE15/77), The Etymologies of the 1930s (Ety/YŌ) and Notes on Names (NN) from 1957 (PE17/170), always with a similar form, meaning and derivation from roots likes √YO(N). Thus it was very well established in Tolkien’s mind.
-ion
son (of), descendant
-ion (patronymic ending) "son (of), descendant" (YŌ/YON, LT1:271, LT2:344). Not to be confused with the genitive ending -on when added to words with nominative plurals in -i, e.g. elenion "of stars" vs. eleni "stars".
Mardil
(one) devoted to the house
Mardil masc. name, "(one) devoted to the house", sc. the "house" of the kings (Appendix A; interpreted in Letters:386). This indicates that the first element can mean "house" in the sense of family or household (see mar, már). This Mardil is described as a good steward, possibly suggesting that mardil ("one devoted to the house/family") could itself function as a common noun "(faithful) steward".
-mo
suffix. agental suffix
-a
suffix. adjectival suffix
This suffix is frequently used to create the adjective form of a noun, especially in the form -ëa for nouns ending in -ë. This function dates back to CE. ✶-ā.
-r(o)
suffix. agental suffix
esse
noun. name
essë
name
essë (1) noun "name", also later name of Tengwa #31, originally (MET) called árë (ázë). (Appendix E). With a pronominal ending esselya "thy name" (VT43:14). Pl. #essi in PM:339 and MR:470, gen.pl. #esseron "of names" in the compound Nómesseron (q.v.); we would rather have expected *ession, given the nom.pl. essi; perhaps #esser is a valid alternative plural form. Essecarmë noun "name-making" (MR:214, 470), Eldarin ceremony where the father announces the name of his child. Essecenta *("k") noun "Name-essay" (see centa) (MR:415); Essecilmë noun "name-choosing", an Eldarin ceremony where a child named him- or herself according to personal lámatyávë (q.v.) (MR:214, 471). The meaning Tolkien originally assigned to the word essë** in the Etymologies was "place" rather than "name" (VT45:12).
essë
noun. name
esta-
verb. name
morion
son of the dark
morion noun "son of the dark" (LT1:261). In Fíriel's Song, Morion is translated "dark one", referring to Melko(r); this may be a distinct formation not including the patronymic ending -ion "son", but rather the masculine ending -on added to the adjective morë, mori- "dark".
sanda
name
[sanda, sandë] (þ) (2) noun "name" (VT46:16)
sanya
name
[sanya] (þ) (2) noun ?"name" (reading of gloss uncertain, VT46:16)
velicë
great
velicë ("k") adj. "great" _(LT1:254; probably not valid in Tolkien's later Quenya; in the context of the Etymologies it would have to be derived from _BEL, but it is stated that this stem was "not found in Q". Perhaps Tolkien rejected velicë because it was too similar to the Russian word that clearly inspired it.)
-n (3) a plural sign used in some of the case endings (WJ:407): Pl. genitive -on, pl. ablative -llon (but also -llor), pl. locative -ssen.