Fill in means to complete a form or document, or to write in missing information: fill in the gaps. The second meaning is to replace a colleague for a short time: fill in for someone.
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fill in + form/gaps; fill it in; fill in for + person; fill sb in (on + news)
- Could you fill in this form and bring it back to reception?
- In this part of the exam, you fill in the gaps with one word only.
- Anna is filling in for Mark while he's on holiday this week.
What changed
First versionPlease fill the application form and send it back by Monday.
RevisionPlease fill in the application form and send it back by Monday.
It is tempting to use fill on its own and write fill the form. But fill without in means to make something full: a glass, a tank, a room. For forms and documents you need the phrasal verb fill in, so the corrected version adds in.
With documents, fill out means the same as fill in, but it is more American: fill out an application. For replacing a person, only fill in for works: Can you fill in for me on Monday? And fill me in means 'tell me what I've missed'.
Your turn
Mr Brown is off sick, so Ms Carter is ___ for him in today's maths lesson.
Show the answer
filling in — The teacher is replacing a colleague who is ill, which is fill in for. Fill out is used only for forms and documents, not for replacing a person.
Imagine you are starting a course or a new job. Write which document you need to fill in and by what date.
Before my first day, I have to fill in a health questionnaire and return it by Thursday.
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