unyielding

adjective

1. unable to bend or be penetrated under pressure; hard: trees so unyielding that they broke in the harsh north winds.
2. not apt to give way under pressure; inflexible; firm: her unyielding faith.

adjective

1. not compliant, submissive, or flexiblehis unyielding attitude
2. not pliable or softa firm and unyielding surface

adj.1590s of persons; 1650s, of substances; from un- (1) “not” + yielding (see yield (v.)).