someone who accompanies another

a person with whom one spends a lot of time

साथी

English Usage: She brought her dog as a companion on the journey.

Hindi Usage: उसने यात्रा पर अपने कुत्ते को साथी के रूप में लाया।

a partner or friend in a specific activity

सहयोगी

English Usage: They decided to be travel companions for the summer.

Hindi Usage: उन्होंने गर्मियों के लिए यात्रा सहयोगी बनने का फैसला किया।