adjective
untold
Too great in amount or extent to measure or describe.
Untold numbers of birds form a dense flock stretching into the distance.

Etymology
Tell once commonly meant count. Untold quantities are uncounted and, by extension, too numerous or extensive to reckon.
In context
Below the bustling streets, an untold number of places [music] lie dormant, sealed by centuries of construction, buried by the relentless accumulation of time.
More examples
- The flood causes untold damage to homes and businesses.
- She spends untold hours caring for injured animals.
- The discovery promises untold benefits for future patients.
Forms
untold
Similar words
- innumerable
- Emphasizes numbers too large to count, rather than overall extent.
- immeasurable
- Emphasizes greatness beyond measurement, especially of feelings or effects.
- incalculable
- Emphasizes amounts or consequences too great to calculate.