The term WINTER PALACE INHABITANT, ONCE is represented by the crossword solution TSAR, which is a four-letter word. TSAR is a title used to refer to a male monarch or emperor in Eastern Europe and Russia. It was used to refer to the Russian rulers from 1547 until 1917, when the monarchy was overthrown and replaced by the Soviet Union. The Winter Palace was the official residence of the Russian Tsars from 1732 until 1917.