The description of the word you requested from the astronomical dictionary is given below.
A moon of 1186 km diameter at about 19,600 km from the planet Pluto. The gravity at its surface is about 0.0313 times as strong as on Earth. The moon goes once around its planet in about 6.9 days. The moon was discovered in 1978. Also called PI (Pluto one). Its provisional designation was S/1978 P1.