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in an unguarded moment
in an unguarded moment 是常见搭配，表示“在一时疏忽/失去警惕之际”。
In an unguarded moment, she let her real feelings show.
她在一时不防的时刻流露了真情。
无防备的；没有防卫的
先理解核心含义，再看它在真实句子里的用法。
无防备的；没有防卫的
lacking protection or a guard
In an unguarded moment, she let her real feelings show.
她在一时不防的时刻流露了真情。
没有防护或保护的；易受伤害的。
Having no guard or protection; vulnerable.
表现出缺乏谨慎或思考的；不留神的。
Displaying a lack of caution or thought.
The unguarded entrance allowed anyone to walk in without being checked.
无人看守的入口让任何人都可以不经过检查就走进来。
Burglars often target unguarded homes during the day.
入室窃贼常常在白天瞄准无人看管的住宅。
The museum's unguarded back door was left open all night.
博物馆无人看守的后门整夜都开着。
in an unguarded moment 是常见搭配，表示“在一时疏忽/失去警惕之际”。
In an unguarded moment, she let her real feelings show.
她在一时不防的时刻流露了真情。
leave + 宾语 + unguarded 表示“使…处于无人看管或没有保护的状态”，宾语常为具体物品。
He left his luggage unguarded at the station.
他把行李留在车站，无人看管。
unguarded 作表语时描述某人或某处处于无防备、没有守卫的状态。
The back door was unguarded all night.
后门整夜都无人看守。
Not this
He unguarded the gate.
Use this
He left the gate unguarded.
“unguarded”是形容词而不是动词。要表达“使某物处于无防备状态”，应使用“leave + 宾语 + 形容词”结构，不能把形容词直接当动词用。
Not this
He made the remark at an unguarded moment.
Use this
He made the remark in an unguarded moment.
“in an unguarded moment”是固定搭配，介词用in而不用at，表示“在一不留神/不设防的时候”。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
不留神的一刻；一时疏忽之际
In an unguarded moment, she let slip her true opinion.
她一时不留神，说出了自己的真实想法。
失言；不谨慎的话
His unguarded remark about the manager caused trouble.
他关于经理的一句失言惹来了麻烦。
无人把守的边境
The refugees crossed the unguarded border at night.
难民们在夜间越过了无人把守的边境。
无人看守的铁路道口
Slow down at this unguarded railway crossing.
经过这个无人看守的铁路道口时要减速。
让某物无人看守
They left the camp unguarded while they went hunting.
他们去打猎时，营地无人看守。
在不留神的时候；一时疏忽之下
In an unguarded moment, he gave away the secret.
他一不留神，把秘密说了出来。
趁某人不备；使某人措手不及
The reporter's question caught the politician unguarded.
记者的问题让这位政客措手不及。
使某物无人看守；疏于防范
She left her purse unguarded on the table and it was stolen.
她把钱包没看管好放在桌上，结果被偷了。
Use unguarded naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
un-（不）+ guarded（守卫/戒备的），想象心里没设防，一时不留神就说了不该说的话。
语域：neutral 常见场景：Physical protection of a place or object、Careless or unwary speech or behavior 该词主要有两个义项：表示“无防卫的、未受保护的”时多用于书面或客观描述；表示“不留神的、不小心的”时常见于 in an unguarded moment、an unguarded remark 等搭配。整体语气偏中性，正式与一般语境都可用。
与 unguarded /ʌnˈɡɑːdɪd/ 真正押韵的词有 guarded /ˈɡɑːdɪd/、regarded /rɪˈɡɑːdɪd/、discarded /dɪsˈkɑːdɪd/、disregarded /ˌdɪsrɪˈɡɑːdɪd/，它们重读音节都含 /ɑːdɪd/。注意 warded /ˈwɔːdɪd/ 虽拼写相近，但元音是 /ɔː/ 而非 /ɑː/，不押韵；candid /ˈkændɪd/ 更不押韵，元音为 /æ/。
Dictionary facts from ECDICT, WIKTIONARY.