-t (1) dual ending, on nouns denoting a pair of something: attat "2 fathers or neighbours" (VT48:19; see atto), máryat "her (pair of) hands" (Nam), siryat "two rivers" (VT47:11), ciriat "2 ships" (Letters:427 – read ciryat as in the Plotz Letter?), maquat "group of ten" (from maqua, meaning among other things "group of five") (VT47:7), nápat "thumb and index as a pair" (VT48:5), also compare met "us two" as the dual form of me "us" (Nam, VT47:11). Other dual endings known from the Plotz letter: genitive -to, possessive -twa, dative -nt, locative -tsë, allative -nta, ablative -lto, instrumental -nten, plus -tes as a possible short locative. It may be that these endings only apply to nouns that would have nominative dual forms in -t, and that nouns preferring the alternative dual ending -u would simply add the otherwise "singular" case endings to this vowel, e.g. *Alduo rather than ?Alduto as the genitive form of "Two Trees" (Aldu). – The ending -t is also used as a verbal inflection, corresponding to pl. -r (elen atta siluvat, “two stars shall shine”, VT49:45; the verb carit “do” would also be used with a dual subject, VT49:16; cf. also the endings listed in VT49:48, 50).
-t (2) "them", pronominal ending; seen in the word laituvalmet "we shall bless them" (lait-uva-lme-t "bless-shall-we-them"). According to PE17:110, this -t covers both sg. and dual. Also independent word te pl. and tú dual (possibly *tu when unstressed).
-t (3) reduced pronominal affix of the 2. person, "you" (sg.), the long form being -tyë (both endings are listed in VT49:48). See heca regarding the example hecat (WJ:364). However, in a later source, Tolkien denies that -tyë has any short form (VT49:51, 57). The status of the ending -t is therefore doubtful.