defend : 普通用词，指用武力或其它措施使人或物不受损害，消除危险。用作比喻时，指坚持某种行动、决定或意见。
- All our officers are trained to defend themselves against knife attacks.
- Politicians are skilled at defending themselves against their critics.
protect : 普通用词，指用某种手段作为防御工具以防危险或伤害。
- Troops have been sent to protect aid workers against attack.
- They huddled together to protect themselves from the wind.
safeguard : 语气强，指采取积极措施预防可能发生的一切攻击或危险。
- to safeguard a person's interests
- to safeguard jobs
- The new card will safeguard the company against fraud.
guard : 普通用词，指保持警惕以防可能的攻击或伤害。
- Gunmen guarded homes near the cemetery with shotguns.
shield : 语气比protect强，但侧重防止迫在眉睫的攻击或伤害。
- He shielded his head from the sun with an old sack.
- He was sensitive and highly-strung, and she had always tried to shield him from his father's sarcasm and violence.
shelter : 通常指寻找安全地方躲避风雨或使人免遭危害。
harbour : 贬义词，指隐匿或非法保护、窝藏。
- Police believe someone must be harbouring the killer.