to fill a gap; to fill in a blank (on a form); to overcome a deficiency

to cram

to fill in a form; to write data in a box (on a questionnaire or web form)

to fill up; to stuff; to fill in a blank space

to feed to the full; to cram

to load; to fill (into a container)

to fill in a form for sb else

to fill (gap, hole, area, blank); to pad out; to complement; (dental) filling; filled

to backfill

sea of hatred is hard to fill (idiom); irreconcilable division