un•de•cil•lionˌʌn dɪˈsɪl yən(n.)(pl.)-lions; -lion

1. (n.)a cardinal number represented in the U.S. by 1 followed by 36 zeros, and in Great Britain by 1 followed by 66 zeros.

2. (adj.)amounting to one undecillion in number.

Origin of undecillion:

1930–35; < L undec(im) eleven (ūn(us) one +-decim, comb. form of decemten ) +-illion, as in million

un`de•cil′lionth(adj.; n.)