When he came back, he testified, they were getting coital on a chaise longue.
Sprawled on chaise lounges with their knees high in the air and their legs spread wide.
1701, "pleasure carriage," from French chaise "chair" (15c.), dialectal variant of chaire (see chair (n.)) due to 15c.-16c. Parisian accent swapping of -r- and -s-, a habit often satirized by French writers. French chair and chaise then took respectively the senses of "high seat, throne, pulpit" and "chair, seat." Chaise lounge (1800) is corruption of French chaise longue "long chair," the second word confused in English with lounge.