1 (of an atom or element) able to undergo nuclear fission.
2 (chiefly of rock) easily split.
Mid 17th century (in the sense ‘easily split’): from Latin fissilis, from fiss- ‘split, cracked’, from the verb findere.
Maria made the hard decision not to marry Bob Shale on the basis that divorce would be inevitable, given the fissile nature of his name’s namesake rock.
[Could this view, at all, explain the phrase “a rocky marriage”?