1. Marked by firm determination or resolution; not shakable
   "a man of unbendable perseverence"
   - firm, steadfast, steady, stiff, unfaltering, unshakable, unwavering, unshakeable

See also: resolute

• Post-Office box
• post-office box number
• post-rotational nystagmus
• postage
• postage meter
• postage stamp
• postal
• postal card
• postal clerk
• postal code
• postal order
• Postal Rate Commission
• postal service
• postal vote
• postbag
• postbiblical
• postbox
• postcard
• postcava
• postcentral gyrus
• postcode
• postdate
• postdiluvian
• postdoc
• postdoctoral