undaunted by; in defiance of; ignoring
Used in the pattern ...をものともせず（に） to describe acting without being deterred by difficulty, danger, or opposition. Often found in formal or literary contexts.
He pushed forward undaunted by the difficulties.
The athlete played in the match in defiance of the injury.
From 物 (もの, 'thing') + とも (emphatic particle) + せず (negative continuative of する, 'do'). Literally 'not making a thing of', i.e., treating something as insignificant.