fill out is a verb meaning "write all the required information onto a form". It carries 6 recorded senses.
supplement what is thought to be deficient
“He eked out his meager pay by giving private lessons”
“Braque eked out his collages with charcoal”
Definitions, synonyms and semantic relations for fill out come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.