@@@ revised glosses suggested by Helge Fauskanger (QQ/ataquanta)
Quenya
ataquanta-
refall, fall second time, double fall
ataquanta-
verb. *to refill, fill a second time, double fill
Elements
Word Gloss at(a)- “double, second time, double, [repeat a] second time; [ᴱQ.] bi-, twi-; [ᴹQ.] back, again, re-” quanta- “to fill, to fill [something], (lit.) make full; [ᴱQ.] to complete, fulfill”
ataquanta- vb. "refall, fall second time, double fall" (sic in PE17:166). The correct gloss must be "refill, fill second time, double fill", which would connect with the verb quanta- "fill" and also make rather better sense.