fill

If you fill something, you put something in it until there is no space left.

Example: She added some games to fill the gap in the schedule.

If you fill in something, you give the missing information, especially personal information on a form.

Example: She gave me another form to fill in for housing benefit.

If you fill out, your body reaches its adult shape, especially women's breasts and men's shoulders.

The full amount of food or drink that a person can eat or drink.

Example: Don't feed him any more, he's had his fill.

Fill is extra material, often of low quality, used to give something more volume.

Example: They used the rocks as fill under the new house.