1. impossible or too difficult to name or describe
2. too terrible or horrible to be spoken of

Examples

• The horror of the tragedy was unnameable.
• She felt an unnameable dread as she entered the abandoned house.
• The artist tried to capture something unnameable in her abstract painting.
• There was an unnameable quality about the old mansion that made visitors uncomfortable.
• The grief he experienced was deep and unnameable.
• Scientists discovered an unnameable species in the deep ocean.
• The unnameable fear kept her awake at night.