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

In her absence, season 1 cohosts Star Jones and Debbie Matenopoulos are set to return to the show as fill-in cohosts, alongside fellow ex-panelists Lisa Ling and cohost Sherri Shepherd. — Joey Nolfi, Entertainment Weekly, 17 Sep. 2026

Okuayinonu, a fill-in starter the past two seasons, practiced Wednesday before a foot injury kept him from joining the 49ers on their charter flight here. — Cam Inman, Mercury News, 5 Sep. 2026

Verb

This is the language the show has used thus far, in that Hal often comes to conclusions and fills in the gaps for us after the fact. — Siddhant Adlakha, Vulture, 28 Sep. 2026

Frazier was shifted from left to right tackle to fill in for Andrew Sprague, who missed a second straight game with an injury. — Arkansas Online, 27 Sep. 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