cautionary

cautionary (comparative more cautionary, superlative most cautionary)

1. Serving to caution or warn; admonitory
2. Serving to ward off; preventive
3. (obsolete) Held as security or hostage

• 2003 Paul Magdalino - Byzantium in the Year 1000

  Constantine's provision seems drawn from recent experience and intended for practical application, rather than being just a form of cautionary tale . . .

• 1715 Casimir Freschot - The Compleat History of the Treaty of Utrecht

  instead of the Cautionary Towns offer'd in the Law Countries, ought to be now contented . . .

• auctionary