From Longman Dictionary of Contemporary Englishfill out phrasal verb1 WRITE fill something ↔ out to write all the necessary information on an official document, form etc2 FATif 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 → fill→ See Verb table
Examples from the Corpus
fill out• Sue looks much healthier now and her face has started to fill out.• Gerry was terribly thin when he came out of hospital, but he's filled out a lot since then.From Longman Business Dictionaryfill something → out phrasal verb [transitive] another name for fill in → fill→ See Verb table 