1. Compétiteur.
2. Rival.
One who challenges.
Orbiter used in the US space shuttle program which on 28 Jan 1986 exploded on takeoff, killing all seven crew members.
Défier.
1. To ask for identification.
2. To issue a challenge to.
3. To raise a formal objection in a court of law; SYN. take exception.
4. To take exception to; SYN. dispute, gainsay.