Late 18th century; earliest use found in Erasmus Darwin (1731–1802), physician and natural philosopher. Either from retract + -ibility, or irregularly from retractable + -ity: see -ibility.
Definition of retractibility in US English:
retractibility
nounrɪˌtraktɪˈbɪlɪti
= retractability.
Origin
Late 18th century; earliest use found in Erasmus Darwin (1731–1802), physician and natural philosopher. Either from retract + -ibility, or irregularly from retractable + -ity: see -ibility.