Ad. -at suf. “dual suffix”
The suffix for dual-nouns in Adûnaic, with the a lengthened to â in subjective duals (SD/428-430). In later (Exhilic?) Adûnaic, the â was long in all cases (SD/431). See the entry on dual-nouns for further details. Carl Hostetter and Patrick Wynne suggested (AAD/11) that -at is derived from the same Primitive Elvish form ✶ata as the Quenya dual.
References ✧ SD/428-429, 431