I Corinthians 16:13 Watch ye, stand fast in the faith, quit (gk. – act)you like men, be strong.
Powerful, mighty, stalwart, vigorous, energetic, sturdy, stout, solid, durable, sound, resolute, determined, tenacious, firm, UNYIELDING, courageous, forceful, intense, fervent, effective, UNDILUTED, extraordinary, extreme, emphatic, severe, HARSH, drastic, radical.