A verb in Quenya Notes (QN) from 1957, a combination of the prefix na- “plu-” with pan- (PE17/146) whose root √PAN means “arrange, set in order” (PE17/108), so more literally “✱arrange with addition”.
Quenya
napan-
verb. add
napan-
verb. to add
yantya-
verb. add, augment
yantya- vb. "add, augment" (PE15:68)
napan- vb. "add" (PE17:146)