imperceptible

imperceptible /ˌɪmpɚˈsɛptəbəl/ adjective
imperceptible
/ˌɪmpɚˈsɛptəbəl/
adjective
Britannica Dictionary definition of IMPERCEPTIBLE
[more imperceptible; most imperceptible]
: impossible to see or notice

— imperceptibly

/ˌɪmpɚˈsɛptəbli/ adverb