The description of the word you requested from the astronomical dictionary is given below.
The General Theory of Relativity by Albert Einstein describes how things are with space and time even when forces act upon the observer. The General Theory of Relativity says that the effects of an acceleration do not depend on the cause of the acceleration (not even if that cause is the force of gravity). It follows that gravity bends rays of light and can slow down time, and that black holes can exist. Einstein invented this theory at the beginning of the 20th century. The theory has passed many tests.