To book something in advance

• To arrange to have a place, service, or item kept for you

To keep something back for future or special use

• To set aside part of a supply

To retain a right or decision for oneself

• To refrain from expressing or deciding now

A supply kept back for future use

• Something saved as a backup

Money set aside to meet expected or unexpected costs

• Regulatory capital held by an organization

Known but undeveloped deposits of oil, gas, or minerals

A tract of land set apart for a particular purpose

• Especially a protected nature or wildlife area

Troops held back to support the main force if needed

A team member not starting, available to replace another

Controlled, cautious manner; lack of openness or warmth

• Self-restraint in words or actions