Zinn in his Zinn and the Art of Road Bike Maintenance says , "One the standard cage-type pedal with a toeclip and strap is the simplest and cheapest. The second, or 'clip-in' type retains the foot with spring-loaded clips......" . "Clip-in pedals are sometimes called 'clipless'. since they have no toeclip."
I personally have been using the term clipin for these modern pedals for as long as I have been aquainted with them.