The Adûnaic name of Númenor after its fall, the equivalent of Q. Atalantë (S/281). Tolkien usually translated this word as “Downfallen”, but its literal meaning was “(She) That Has Fallen” (PE17/111, SD/247). The final element -êth seems to be a feminine suffix, also seen in Arminalêth. The middle element -kallab- seems to be the past formation kallaba of the verb kalab- “to fall (down)”. The function of the initial a- isn’t clear, but it may be some sort of perfective augment, as seen in the Quenya perfect tense; see the discussion of the Adûnaic draft-perfect for more information.
Other Interpretations: Carl Hostetter and Patrick Wynne suggested (VSH/36) that the prefix a- is probably some kind of emphatic suffix rather than evidence of another verb tense. Thorsten Renk proposes (NBA/39) that the a- is a relative pronoun “that”, analogous to Q. ya, which is an interesting possibility.