infinite time; duration without beginning or end.

eternal existence, esp. as contrasted with mortal life

the eternity of God.

Theology . the timeless state into which the soul passes at a person's death.

an endless or seemingly endless period of time

We had to wait an eternity for the check to arrive.

eternities, the truths or realities of life and thought that are regarded as timeless or eternal.

noun

aeon , afterlife , age , ages , blue moon * , dog’s age , endlessness , endless time , everlastingness , forever and a day , future , immortality , imperishability , infiniteness , infinitude , infinity , kingdom come * , other world , perpetuity , timelessness , time without end , wild blue yonder , world without end * , eternality , eternalness , sempiternity , ceaselessness , world without end , deathlessness , everlasting life , eon , long , year , blue moon , forever