INVISIBLE

[adjective] [not gradable] - impossible to seeMost spiders weave webs that are almost invisible.The Stealth fighter is an aircraft designed to be invisible to radar.These bacteria live in a soft, almost invisible, film called plaque which coats the teeth.Marks that are invisible to the eye are made visible using a new technique.The scheme aims to boost the country's invisible exports (= services supplied to foreign countries such as banking, rather than goods such as machines).It looked like a blank sheet of paper but there was a message on it in invisible ink (= ink which can not be seen until it is treated with chemicals or heat).