1. The ordinal number matching the number decillion in a series.
2. One of a decillion equal parts.

de·cil′lionth adv. & adj.
References in periodicals archive ?
SECOND = Sixty-Eight Centillion One Ninety Decillionth & Seventy-Eight Centillion One Ninety Duodecillionth.
Extraordinary flatness means the universe experienced relatively prolonged inflation, up to a decillionth of a second or more, immediately after the big bang.