1) Adamant 2) Constant 3) Determined 4) Firm 5) Foursquare 6) Hardcore 7) Iron 8) Obstinate 9) Permanent 10) Resolute 11) Set 12) Solid 13) Steadfast 14) Steady 15) Steely 16) Sure 17) True 18) Unbendable 19) Unfaltering 20) Unhesitating 21) Unshakable 1) Committed 2) Dedicated 3) Firm 4) Not shakable 5) Not showing abrupt variations 6) Persistent 7) Resolute 8) Steadfast 9) Steady 10) Unbendable 11) Unfaltering 12) Unshakable 13) Unswerving 
marked by firm determination or resolution marked by firm determination or resolution[SAT terms] marked by firm determination or resolution; not shakable