The term 'HAPPY, AS BYGONE DAYS' can be solved by the crossword solution 'HALCYON', which is a seven-letter word. HALCYON is derived from Greek mythology and refers to a bird that was said to have the power to calm the wind and waves during the winter solstice. It has come to mean a time of peace and tranquility, and is often used to describe a period of time in the past that was particularly happy and carefree.