undated

As a noun taxonomy

is the science or the technique used to make a classification.

As an adjective undated is

not marked with a date or undated can be (botany) rising and falling in waves toward the margin, as a leaf; waved.

Nondated is a synonym of undated.

As adjectives the difference between undated and nondated

is that undated is not marked with a date while nondated is not marked with a date.

As an adjective undated

is not marked with a date or undated can be (botany) rising and falling in waves toward the margin, as a leaf; waved.

As a noun datelessness is

the state or condition of being dateless: timeless or undated.