adverb
in an imperceptible manner or to an imperceptible degree (Freq. 1)
-
the power of the Secretary of State in London increased gradually but imperceptibly
• Syn: ↑unnoticeably
• Ant: ↑perceptibly
• Derived from adjective: ↑unnoticeable (for: ↑unnoticeably), ↑imperceptible
Useful english dictionary. 2012.