fill in

to do someone else's work for them because they cannot or will not do it themselves:
She will fill in for him while he's at the conference.
I'm not her regular secretary - I'm just filling in.
(Cambridge Advanced Learner's Dictionary & Thesaurus からの fill in の定義 © Cambridge University Press)

アメリカ英語辞典
to do someone else’s job temporarily:
The gym teacher was sick today, so a substitute filled in for her.
(Cambridge Academic Content Dictionary からの fill in の定義 © Cambridge University Press)

ビジネス英語
fill in
— phrasal verb with fill verb [ T ]
UK /fɪl/ US

[ T ]
to write or type information on a document in spaces that are provided for it:
Companies will encourage customers to fill in questionnaires about themselves.
Please print off a copy of the agreement, fill it in, sign it and send it back.

[ I ]
to do the work of someone else for a short time:
fill in for sb I asked Agnes to fill in for me while I went for lunch.
When you're off sick, someone else has to fill in.

[ T ]
to tell someone something they do not know, especially something that happened when they were not there:
I haven't seen the latest report, so perhaps you could fill me in?
fill sb in on sth Josh filled me in on what had been agreed at the meeting.

(Cambridge ビジネス英語辞典 からの fill in の定義 © Cambridge University Press)

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