I first heard the word teep, short for telepath, on the TV show Babylon 5 in 1994 or so. Until today, I thought the word had been invented for the show.
But I just happened across it in a Philip K. Dick story, “The Hood Maker,” that was written in 1953 and published in 1955, predating the B5 usage by about 40 years.
Dick defines the word shortly after using it for the first time in the story (“Ernest Abbud was a telepathic mutant—a teep”), so I’m guessing he didn’t expect it to be widely understood without a definition. (Dick didn’t always define his coinages; for example, there are stories in which he uses the terms robant (robot servant) and homeopape (homeostatic newspaper) without defining them.)
Wiktionary gives another Dick citation for teep: his novel Solar Lottery, also published in 1955. But I haven’t found any earlier citations.
So I’m guessing that Dick coined the word in 1953 or so. But I’d be interested in hearing any citations from earlier than that.