The crossword solution for the term 'Tidal Adjective' is NEAP, which is an adjective meaning 'occurring twice in a lunar month, especially at the first and third quarters of the moon.' This term is used to describe the tides, which are the rise and fall of the ocean's water level due to the gravitational pull of the moon and sun. NEAP tides occur when the gravitational pull of the moon and sun are at right angles to each other, resulting in lower than average tides.