aiōn

At its root this word names time as a vast extent. Depending on context it points to a measured span (an era with a beginning and an end), to time with no limit (the everlasting), or to the whole arena of created time and the world as it runs its course. The Greek word had traveled a long road before the New Testament: from a person's lifetime in the oldest poetry, to a philosopher's word for timeless eternity, and then, through the Greek Old Testament, to the standard rendering of the Hebrew word for the far horizon of time (עולם).

The New Testament leans hard on three uses. The first divides history into two great epochs: the present age, marked by sin and passing away, set against the age to come, the kingdom that will not pass. This two-age framework, inherited from Jewish writings of the period, is the dominant way the word does theological work. The second use is the set phrase rendered "forever," where the word stops measuring a span and instead pictures duration that never runs out, often doubled and piled up in worship as "to the ages of the ages." The third use shades from time into the world itself, the present order so dominated by evil that it can be called the realm whose god has blinded people.

These senses are not separate words but facets of one idea: time conceived as a sweep. The same term can frame a single era, the endlessness of God, or the world living out its allotted time. The reader has to let the context decide whether a fixed period, sheer perpetuity, or the present world is in view, and resist collapsing all its shades into a single English word.