The term 'lessen in intensity' can be described by the crossword solutions of WANE, BATE, EASE, and ABATE. WANE means to gradually decrease in size, strength, or intensity over time. BATE means to reduce or lessen in intensity or degree. EASE means to make something less difficult or intense. Finally, ABATE means to reduce in intensity or degree, especially gradually. All of these words describe a process of decreasing intensity or degree, which is what the term 'lessen in intensity' implies.