-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
suffix. masculine suffix
-on
suffix. augmentative, great
-on
name
-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".
-mo
suffix. agental suffix
A suffix of which Tolkien said “the ending -mo often appeared in names or titles, sometimes with an agental significance” (WJ/400). It is based on the pronoun mo “(some)one”. This suffix is often specifically neuter, as in [ᴹQ.] nilmo “friend” vs. male and female [ᴹQ.] nildo and nilde (Ety/NIL).
Conceptual Development: The suffix ᴱQ. -mo appears all the way back in the Qenya Lexicon of the 1910s in words like ᴱQ. laulemo “inhabitant” and ᴱQ. qolimo “invalid” (QL/52, 78).
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".
-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
An agental suffix derived from ancient ✶-rō̆ (WJ/371), usually appearing as suffixal -r but sometimes as -ro as in quentaro “speaker, minstrel” (PE19/83; PE18/51). The fuller form appears especially in cases where the word is taken to be masculine: compare its feminine form [ᴹQ.] quentare “minstrel [f.]” (PE23/85). Tolkien indicated -rō was sometimes accompanied by nasal infixion, and that there was another variant -rdŏ > rd (WJ/371), but there are no clear signs of -r(d) in his later writings (but see the ᴱQ. examples below).
Based on the example ontari “parents” plural of [ᴹQ.] ontaro “parent [m.]”, it seems the usual plural form of this suffix may be -ri even in cases where -ro survived into Modern Quenya. This plural could be because of Quenya’s general dislike of repeated r-sound. However, ontaro may also be a specifically masculine form of an unattested gender neutral ✱ontar “parent” and ontari may be the plural of that gender neutral form, in which case likely there is no plural for the specifically masculine form. Regardless of the exact phenomenon in play, I would assume the plural of words like quentaro “minstrel” is quentari, referring to a group of minstrels of any gender.
Conceptual Development: There are no examples of -ro in the Early Qenya of the 1910s and 20s, but there are examples of agental -r and sometimes -ar, as in ᴱQ. maksar “cook” from ᴱQ. maksa- (QL/59), and ᴱQ. vaktelear “merchant” from ᴱQ. vaktele “trade” (QL/99). There are also examples of -r(d), such as ᴱQ. ektar (ektard-) “swordman” (QL/35) and ᴱQ. moar (moard-) “shepherd” (QL/60).
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.