Answer:

agonist

Answer	Crossword Clue
AGONIST	One in a conflict
AGONIST	One in a struggle
AGONIST	Competitor or contestant

AGONIST	Person in a conflict
AGONIST	One struggling
AGONIST	Participant in a struggle
AGONIST	Contracting muscle
AGONIST	One engaged in a struggle

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.