The term IDITAROD NECESSITY is composed of two words, the first being 'IDITAROD' and the second being 'NECESSITY'. The crossword solution for the first word is 'SLED', which is a four-letter word. A SLED is a vehicle used to transport goods or people over snow or ice, and is an essential tool for participating in the Iditarod Trail SLED Dog Race, an annual long-distance SLED dog race held in Alaska. The second word, 'NECESSITY', refers to the fact that sleds are necessary for competing in the Iditarod Trail SLED Dog Race.