ankylosing spondylitis Syllabification: (an·ky·los·ing spon·dy·li·tis)Pronunciation: /ˈaNGkəˌlōsiNG ˌspəndlˈītis, -ˌlōziNG/Definition of ankylosing spondylitis noun Medicine a form of spinal arthritis, chiefly affecting young males, that eventually causes ankylosis of vertebral and sacro-iliac joints. ankylosing spondylitis in other Oxford dictionaries Definition of ankylosing spondylitis in the British & World English dictionary