This is one of 22,889 words and senses marked in the Oxford English Dictionary as being both obsolete and rare. The OED’s only record for it is from a work of 1646 by the physician Sir Thomas Browne. He’s immortalised in the OED by 3792 other citations, which include many equally rare words, such as bicipitous (having two heads); elychnious (having the nature of a wick); latirostrous (broad-beaked); stillicidious (falling in drops); and zodiographer (a person who writes about animals).
Cenatory, relating to dinner or supper, isn’t quite so rare as the OED entry might suggest. It turns up, for example, in Camp-Fire and Cotton-Field, by Thomas W. Knox, published in 1865: “On one line of boats, the cold meats on the supper-table were from carefully selected pieces, cooked and cooled expressly for the cenatory meal.” And it’s in James Branch Cabell’s Chivalry (1921), in a passage that follows a description of a meal: “Richard was replete and contented with the world. He took up the lute, in full consciousness that his compliance was in large part cenatory.”
Cenatory is from Latin cenatorius, relating to dinner. It has a similar meaning to prandial (Latin prandium, meal), which the OED describes as “affected or jocose” and which usually appears in the compounds pre-prandial, before dinner (sometimes also ante-prandial), and post-prandial, after the meal. (“He went through dinner talking on such events of the time as usually form the subject of prandial conversation.” — The Man Who Bought London, by Edgar Wallace, 1915.)