someone who competes, especially in a contest or competition

प्रतिभागी

English Usage: She is a skilled contester in the annual chess tournament.

Hindi Usage: वह वार्षिक शतरंज प्रतियोगिता में एक कुशल प्रतिभागी है।

to challenge or dispute something

चुनौती देना

English Usage: He decided to contester the election results due to alleged irregularities.

Hindi Usage: उसने कथित अनियमितताओं के कारण चुनाव परिणामों को चुनौती देने का निर्णय लिया।