talta- vb. "slip, slide down, collapse, slope" (TALÁT); reduplicated stem in the participle talta-taltala in Markirya, simply translated "falling" in MC:215. Strong intransitive conjugation: present talta, aorist talt- [derived from talati > talti, hence presumably *talti*- with endings and taltë without any], past talantë, perfect ataltië. Weak transitive conjugation: present taltëa, aorist talta, past taltanë**. This is said to be the conjugation type of a certain class of verbs, namely "√TALAT stems" (PE17:186).
Quenya
ataltare
noun. collapse
atalta-
collapse, fall in
talta-
slip, slide down, collapse, slope
talta-
verb. to slip, slide down, fall, to slip, slide down, collapse, fall, [ᴹQ.] slip down, slope
atalantë
noun. collapse, downfall
atalante
verb. collapsed
collapsed, fell down
atalantë
downfall, overthrow, especially as name [atalantë] of the [downfallen] land of númenor
atalantë noun "downfall, overthrow, especially as name [Atalantë] of the [downfallen] land of Númenor" (DAT/DANT, TALÁT, Akallabêth, SD:247, 310; also LR:47, VT45:26). Variant atalantië "Downfall", said to be a normal noun-formation in Quenya (Letters:347, footnote). From the common noun atalantë "collapse, downfall" is derived the adj. atalantëa "ruinous, downfallen", pl. atalantië in Markirya (changed to sg. atalantëa this change does not make immediate sense, since the adjective undoubtedly modifies a plural noun, but Tolkien does not always let adjectives agree in number).
atalat-
verb. slip right down
slip right down, collapse, fall in ruin
talta-
verb. slip, fall
atalta- vb. "collapse, fall in" (TALÁT), weak pa.t. ataltanë "down-fell, fell down" in LR:47 and SD:247, but strong past tense atalantë "down-fell" in LR:56