The term 'FULL MOON OR NEW MOON' refers to the two phases of the moon's cycle. The answer to the crossword is 'PHASE, ' which is a five-letter word. A full moon occurs when the moon is completely illuminated by the sun, while a new moon occurs when the moon is not visible from Earth due to its position in relation to the sun. The full moon and new moon phases occur at different points in the moon's orbit around the Earth.