Unlike the modern use of the noun hypochondria, as an abstract singular meaning a morbid fixation on one's health, here it is a neuter plural with a strictly anatomical application. For the etymology cf. chi 391.
Likewise or similarly in other lexica; references at Photius upsilon281, where Theodoridis cites Naber's view that the headword is quoted from 1 Kingdoms 31.3 LXX; cf. already under delta 95, on the death of Saul.
[1] Term attested only in these lexica.