The term 'EXTREMELY SERIOUS' can be described by two crossword solutions: SOLEMN (6 letters) and DIRE (4 letters). SOLEMN is an adjective that means having a serious and dignified manner or character. It is often used to describe a SOLEMN occasion, such as a funeral or a religious ceremony. DIRE is an adjective that means extremely serious or urgent. It is often used to describe a situation that is desperate or direly in need of attention. Both words are used to describe a situation that is very serious and requires immediate attention.