-li partitive pl. ending (simply called a plural suffix in the Etymologies, stem LI). The ending is used to indicate a plural that is neither generic (e.g. Eldar "the Elves" as a race) nor definite (preceded by article); hence Eldali is used for "some Elves" (a particular group of Elves, when they are first mentioned in a narrative, VT49:8). Sometimes Tolkien also lets -li imply a great number; in PE17:129, the form falmalinnar from _Namárië _is broken down as falma-li-nnar "foam wave-many-towards-pl. ending", and falmali by itself Tolkien translated "many waves" (PE17:73). A distinct accusative in -lī seems to occur in the phrase an i falmalī (PE17:127, apparently meaning the same as i falmalinnar, but replacing the allative ending with a preposition). Genitive -lion in vanimálion, malinornélion (q.v. for reference), allative -linna and -linnar in falmalinnar, q.v. The endings for other cases are only known from the Plotz letter: possessive -líva, dative -lin, locative -lissë or -lissen, ablative -lillo or -lillon, instrumental -línen, "short locative" -lis. When the noun ends in a consonant, r and n is assimilated before l, e.g. Casalli as the partitive pl. of Casar "Dwarf" (WJ:402), or elelli as the partitive pl. of elen "star" (PE17:127). It is unclear whether the same happens in monosyllabic words, or whether a connecting vowel would be slipped in before -li (e.g. ?queneli or ?quelli as the partitive pl. of quén, quen- "person").
Quenya
-is
respective
-li
the elves
-ssë
respective
-s (2) ending for the mysterious case sometimes called "respective", actually probably a shorter variant of the locative in -ssë. Pl. -is, dual -tes, partitive pl. -lis.
-is ending for the plural form of an unidentified case, by some called "respective" or "short locative" (Plotz)