The term 'EXTREMELY SIGNIFICANT' can be summarized by two crossword solutions: EPOCHAL and MSXITKH. EPOCHAL is an adjective meaning 'of, relating to, or marking an epoch or a period of time in history'. MSXITKH is an adjective meaning 'very important or significant'. Together, these two words provide a comprehensive description of the term EXTREMELY SIGNIFICANT, which can be defined as having great historical importance or being of great significance.