The term "Solunar" was coined by the late, great sportsman John Alden Knight in 1926. He created it to identify his refinement of the old folk theory "Moon Up -- Moon Down" to identify the most productive times to hunt and fish. According to this theory, the best results in were obtained when the moon was either directly overhead or directly underfoot.
Knight's refinement involved the systematic evaluation of a list of 33 factors which then were thought could affect the behavior of fish and game. This list was eventualy pared down to three: the sun, the moon, and the tides. The affects of each were eventually codified into his Solunar Tables, first published in 1936, and still in use today.
Knight authored numerous books and magazine articles on the topics of fishing and hunting, was a championship caliber fly-caster and wing-shot, and was regarded as the dean of sportsmen in his day. Knight died on April 8, 1966 in Florida.
Good luck, and good shooting (and fishing) using Knight's Solunar Tables!