imperceptible

adjective
     
im‧per‧cep‧ti‧ble
almost impossible to see or notice:
Such changes are imperceptible to even the best-trained eye.
imperceptibly adverb:
The daylight faded almost imperceptibly into night.
imperceptibility noun [uncountable]

Dictionary results for "imperceptible"
Dictionary pictures of the day
Do you know what each of these is called?
What is the word for picture 1? What is the word for picture 2? What is the word for picture 3? What is the word for picture 4?
Click on any of the pictures above to find out what it is called.