1
the rearguard + [singular verb]
rearguard 是集合名词，作主语时谓语动词常用单数。
The rearguard fought bravely to slow the enemy's advance.
后卫部队英勇作战，以减缓敌人的推进。
后卫部队
rearguards — plural of rearguard
先理解核心含义，再看它在真实句子里的用法。
后卫部队
a military unit that protects the rear of an army, especially during a retreat
The rearguard fought bravely to slow the enemy's advance.
后卫部队英勇作战，以减缓敌人的推进。
部队的最后部分,尤指保护撤退部队后方的分遣队。
The rearmost part of a force, especially a detachment of troops that protect the rear of a retreating force.
负责保护(撤退中)军队后方的分遣队
a detachment assigned to protect the rear of a (retreating) military body
后卫；全体防守队员。
The defence, collectively the defenders.
The general ordered the rearguard to hold the bridge while the main army crossed the river.
将军命令后卫部队守住桥梁，而主力部队则过河。
After the retreat began, the rearguard fought bravely to slow down the enemy's advance.
撤退开始后，后卫部队勇敢作战，以减缓敌人的推进。
The army's rearguards took turns covering the retreat through the mountain pass.
军队的各支后卫部队轮流掩护撤退通过山口。
rearguard 是集合名词，作主语时谓语动词常用单数。
The rearguard fought bravely to slow the enemy's advance.
后卫部队英勇作战，以减缓敌人的推进。
of 后接被掩护的队伍，如 army、convoy、column。
The rearguard of the convoy was ambushed.
车队的后卫部队遭到了伏击。
He was placed in the rearguard during the retreat.
撤退期间，他被安排在后卫部队中。
Not this
The back guard covered the army's retreat.
Use this
The rearguard covered the army's retreat.
汉语的“后卫”直译成 back guard，但英语军事术语固定用 rearguard（也可写作 rear guard）表示掩护撤退的后卫部队；back guard 不是地道的英语表达，所以应改为 rearguard。
Not this
The vanguard stayed behind to protect the retreating soldiers.
Use this
The rearguard stayed behind to protect the retreating soldiers.
vanguard 指军队的前锋或先头部队，而 rearguard 才指负责殿后、掩护撤退的后卫部队。句子说 stayed behind（留在后面），所以应改用 rearguard。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
后卫行动；后卫战
They fought a rearguard action to delay the enemy.
他们进行后卫战以拖延敌人。
后卫部队
A rearguard force covered the retreat of the main army.
一支后卫部队掩护主力部队撤退。
后卫阵地
The soldiers held a rearguard position while the civilians escaped.
士兵们坚守后卫阵地，同时让平民撤离。
后卫指挥官
The rearguard commander gave the order to withdraw.
后卫指挥官下令撤退。
为拖延或阻止不利结果所做的最后努力；最后的抵抗
The protesters mounted a rearguard action against the demolition of the old theater.
抗议者为阻止拆除老剧院做了最后的抵抗。
进行最后的抵抗，竭力阻止（不可避免的）失败
Local residents are fighting a rearguard action to keep the historic bridge open.
当地居民正在进行最后的努力，力求保住这座历史悠久的桥梁。
Use rearguards naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
rear（后方）+ guard（守卫）→ 后卫部队，撤退时保护队伍后方的士兵。
语域：formal 常见场景：military history、formal writing、tactical discussions 该词为军事术语，通常用于正式或历史语境，指撤退时掩护后方的部队。日常口语中较少使用。
rearguard /ˈrɪəɡɑːd/ has stress on the first syllable, so no common word is an exact rhyme. The -guard words (guard, vanguard, bodyguard, lifeguard) match the spelling and the unstressed final /ɡɑːd/, but their stressed syllables differ. guard, hard and regard form a genuine rhyme group because they all have stress on the same /ɑː/ vowel: /ɡɑːd/, /hɑːd/, /rɪˈɡɑːd/. Beware regard: it is spelled like 'rear + guard' but pronounced /rɪˈɡɑːd/ with stress on the second syllable, not /ˈrɪəɡɑːd/.
Dictionary facts from ECDICT, WIKTIONARY.