锐气 is the energetic, edge-of-the-blade kind of spirit — fresh, aggressive, ready to charge. Often paired with verbs of dulling: 挫锐气 ("blunt the fighting spirit"), 锐气大减 ("morale greatly diminished").
memory
锐 = sharp (the metal radical 钅 + 兑); 气 = spirit/energy. So literally "sharp energy" — the keenness of a freshly honed blade applied to a person's drive.
