Determined:
— Single-minded in his determination to stop smoking.

synonym: resolved.

Roget 703: artless, natural, pure, native, confiding, simple, lain, inartificial^†, untutored, unsophisticated, ingenu^†, unaffected, naive; sincere, frank; open, open as day; candid, ingenuous, guileless; unsuspicious, honest etc. 939; innocent etc. 946; Arcadian^†; undesigning, straightforward, unreserved, aboveboard; simple-minded, single-minded; frank-hearted, open-hearted, single-hearted, simple-hearted.    free-spoken, plain-spoken, outspoken; blunt, downright, direct, matter of fact, unpoetical^†; unflattering.    ... show more