fill out phrasal verb ( see also ↑ fill )
1 . fill something ↔ out to write all the necessary information on an official document, form etc
2 . if you fill out, or your body fills out, you become slightly fatter:
Eric has filled out around the waist.
3 . if a young person fills out, their body becomes more like an adult’s body, for example by having bigger muscles, developing breasts etc:
At puberty, a girl’s body begins to fill out.
4 . fill something ↔ out to add more details to a description or story