adjective
imperceptible
im-pur-SEP-tuh-buhl/ˌɪmpərˈseptəbl/
Too slight or subtle to be noticed.
The tiny ripple is nearly imperceptible until the magnified view reveals it.

Etymology
The pieces mean “not capable of being perceived.” In the selected sense, something may exist or happen but be too slight to register with the senses.
In context
The movement is subtle, almost imperceptible, yet continuous. Never twice does the same thing appear at this lake.
More examples
- The difference between the two shades is almost imperceptible.
- She gives a nearly imperceptible nod.
- The crack is imperceptible to the naked eye.
Forms
imperceptible
imperceptibly adverb — In a way that escapes notice.
Similar words
- subtle
- Difficult to notice, but not necessarily beyond human perception.
- undetectable
- Emphasizes inability to discover something through observation or testing.