Rival adjectives are listed in this post. Each word below can often be found in front of the noun rival in the same sentence. This reference page can help answer the question what are some adjectives commonly used for describing RIVAL.
ai, ambitious, american, ancient, big, biggest, bitter, chief, close, closest, commercial, dangerous, deadly, democratic, detested, dreaded
early, economic, english, envious, european, fair, famous, favoured, foreign, former, formidable, fortunate, french, friendly, future, generous
german, great, greater, greatest, happy, hated, haughty, ideological, illustrious, imperial, important, jealous, late, literary, longtime, main
major, maritime, mean, mighty, military, natural, nearest, new, northern, old, older, only, other, own, personal, political
popular, possible, potent, potential, powerful, primary, principal, professional, proud, real, republican, romantic, serious, sole, strong, stronger
successful, supposed, time, traditional, triumphant, troublesome, unfortunate, unsuccessful, unworthy, victorious, worthy, young, younger, youthful
Hope this word list had the adjective used with rival you were looking for. Additional describing words / adjectives that describe / adjectives of various nouns can be found in the other pages on this website.