If you fill in for someone, you do the work or task that they normally do because they are unable to do it. Vice-presidents' wives would fill in for first ladies. = stand in
If you fill in a shape, you cover the area inside the lines with colour or shapes so that none of the background is showing. When you have both filled in your patterns, you may want to share these with each other With a lip pencil, outline lips and fill them in
If you fill someone in, you give them more details about something that you know about. I didn't give Reid all the details yet -- I'll fill him in He filled her in on Wilbur Kantor's visit
If you fill in a form or other document requesting information, you write information in the spaces on it. If you want your free copy of the Patients' Charter fill this form in Fill in the coupon and send it first class to the address shown. = fill out
If you are filling in time, you are using time that is available by doing something that is not very important. That's not a career. She's just filling in time until she gets married. see also fill 3
write all the required information onto a form; "fill out this questionnaire, please!"; "make out a form"