Japanese (and Korean) cameras and lenses

The brand name PENTAX comes from the contraction of Pentaprisma-Contax. Registered by Zeiss-Ikon (Dresde) on may 25th, 1952 for their products. After final adoption of mark PENTACON, it was sold to Asahi Optical Co, which became Asahi-Pentax, generally known under the name Pentax (Source: http://www.zenitcamera.com/archive/history/marks.html, Google automatic translation)
Another explanation: The previous models of Asahi Optical Co were called Asahiflex, the first model with pentaprism was called Pentax, contraction of Pentaprism Asahiflex. This name was retained for the following models, up to replace the Asahi brand. But as Zeiss-Ikon had already registered the name Pentax, in particular in South Africa, the bodies sold in this country were called Pentar. Until the name was acquired from Zeiss-Ikon.
A lot of informations on the site of the Asahi Optical Historical Club: www.aohc.it.