Here are some synonyms for imperceptible:
* Unnoticeable
* Undetectable
* Inconspicuous
* Faint
* Gradual
* Minimal
Example Sentences:
* The change in temperature was imperceptible at first, but it gradually became colder.
* Her smile was imperceptible to the casual observer.
* The sound of the clock ticking was imperceptible in the quiet room.
Think of it like this: If something is imperceptible, it's like it's not even there, because it's too small or subtle to be seen, heard, or felt.