Wiktionary
vb. 1 (context transitive English) To fill; to replace material that is absent or has been removed. 2 (context transitive idiomatic English) To inform somebody, especially to supply someone missing or missed information. 3 (context intransitive idiomatic English) To substitute for somebody or something. 4 (context transitive English) To complete a form or questionnaire with requested information.
WordNet
v. supply with information on a specific topic; "He filled me in on the latest developments"
represent the effect of shade or shadow on [syn: shade]
be a substitute; "The young teacher had to substitute for the sick colleague"; "The skim milk substitutes for cream--we are on a strict diet" [syn: substitute, sub, stand in]
write all the required information onto a form; "fill out this questionnaire, please!"; "make out a form" [syn: complete, fill out, make out]
Usage examples of "fill in".
He could fill in the blanks for her, and, he admitted, for himself.
We always have a few spare columns on the hook to fill in when one of these things comes up.
But highbrows like Stinky will be going back to Mars for a century to fill in what I never learned.
She intended to feed a report to her commander by mid-morning and had several blanks she wanted to fill in first.
But the minute Pandora was out of the picture, she called Leonardo and offered to fill in.