The description of the word you requested from the astronomical dictionary is given below.
planètès astèr = [Greek] wandering star; kentrum = [Greek] middle, center
Planetocentric means: with a planet at the center, or relative to the center of a planet. Planetocentric coordinate systems have the center of the planet for origin, and are almost always rectangular coordinate systems, but vary in the directions of the coordinate axes. Oft-used planetocentric coordinate systems are the planetocentric equatorial coordinate system and the planetocentric ecliptic coordinate system.