Early 17th century; earliest use found in Richard Sheldon (d. ?1642). From post-classical Latin defectibilis liable to fail from classical Latin dēfect-, past participial stem of dēficere + -ibilis.
Definition of defectible in US English:
defectible
adjectivedɪˈfɛktəbl
Liable to fail or fall short; fallible.
Origin
Early 17th century; earliest use found in Richard Sheldon (d. ?1642). From post-classical Latin defectibilis liable to fail from classical Latin dēfect-, past participial stem of dēficere + -ibilis.