fill sth in
phrasal verb.phrasal verb. To write information in the empty spaces on a form or document.
phrasal verb. To add required information to the blank spaces of a document, form, or questionnaire. This transitive phrasal verb is separable.
Please fill in this form with your details.
You need to fill in your name and address on the first page of the application.
The historian had to carefully fill in the gaps in the manuscript, using contextual clues from other contemporary sources.
Commonly used for forms, applications, and documents that have blank spaces for information.
Contrast with 'fill out', a near-synonym in American English; 'fill in' can focus on specific blanks, while 'fill out' often implies completing the entire document.
Please fill the form.Please fill in the form.The particle 'in' is required to form the phrasal verb meaning 'to complete'.
Last updated April 24, 2026