fill-in

1 of 2

noun

ˈfil-ˌin 

: someone or something that fills in

She performed well as the emergency fill-in.

fill in

2 of 2

verb

filled in; filling in; fills in

transitive verb

1

: to enrich (something, such as a design) with detail

2

: to give necessary or recently acquired information to

I'll fill you in

intransitive verb

: to fill a vacancy usually temporarily

Interns filled in for regular staffers.

Synonyms of fill-in

Noun

• substitute
• replacement
• backup

Verb

• inform
• tell
• advise
• catch up

Examples of fill-in in a Sentence

Noun

I'm just a fill-in, so I have no idea where office supplies are kept

Verb

my friend quickly filled me in on the portion of the movie that I had missed

she's only filling in while the regular secretary is on vacation

Recent Examples on the Web

Noun

The fill-in starting right guard was in the midst of his most impressive stretch as a pro when his right Achilles ruptured in the Panthers’ blowout loss. — Charlotte Observer, 7 July 2026

Ski, who previously worked at V-103 from 1998 to 2012 and from 2018 to 2020, rejoined the station in May as a weekend and fill-in host. — Rodney Ho, AJC.com, 6 July 2026

Verb

Before a ball was even kicked at this tournament, many people predicted this semifinal matchup when filling in their bracket. — Aleks Klosok, CNN Money, 10 July 2026

Upon returning to Earth, the crew of Apollo 11 had to fill in a customs form at Honolulu Airport to declare their cargo of Moon rocks and samples. — Elijah Tan, Encyclopedia Britannica, 10 July 2026

Word History

First Known Use

Noun

1917, in the meaning defined above

Verb

1840, in the meaning defined at transitive sense 1

Rhymes for fill-in

• akin
• auxin
• buckskin
• chagrin
• crankpin
• deerskin
• foreskin
• fuchsin
• herein
• kingpin
• linchpin
• pigskin

Kids Definition

fill in

verb

1

: to furnish with specified information

fill in an application

filled us in on the latest news

2

: to fill a vacancy usually temporarily : substitute

filled in during the emergency