Including, of chemical bonds, splitting easily, but the word's natural domain is much wider than chemistry. Not to be confused with fissile, which is capable of being cloven, a much stronger action, or sessile, which is attached or fixed at the base. Borrowed around 1620 from Latin scissilis, from scissus, past participle of scindere, to split, and thus cogante to scission and scissors. The sc- words, they do scintillate around here.
A chemical bond is weak and so called scissile, but a nuclear bond is strong and so fissile, when it can be fissioned at all.