light a fire under

verb

"light-a-fire-under" is a 15-letter English headword indexed on PlainSpell.

The verdict

“light a fire under” is uncommon English (outside the top frequency list), classed as a verb. The kind of spelling people second-guess.

Unranked
below top-frequency English
18
letters

According to Wiktionary data (CC BY-SA, analyzed September 3, 2026) - To motivate or encourage (someone) to start sooner or move faster.

Corpus desk

Index EN-light-a-fire-under · light a fire under · English

light a fire under · unranked · 0 variants · 0 confusables

  • FREQ-UNRANKED Unranked
  • LEN-MEGA 18 letters
  • VOW-6 6 vowels
  • CONFUS-0 No pairs
  • VAR-0 0 variants
  • BOOK-THIN "L" thin
  • PHOTO-UNK Peer pending

Read with this headword: Spelling guide for this pattern

Desk codes from Wiktionary headword shape, FrequencyWords rank tier, confusable-pair count, generated misspelling depth, letter-cohort book size, and photo-finish peer. Not a difficulty grade.

Key facts for light a fire under
PropertyValue
Headwordlight a fire under
LanguageEnglish
Part of speechVerb
Letters18
Misspellings tracked0
Confusable pairs0
SourceWiktionary (kaikki.org)

Long-tail rank of “light a fire under” in English

light a fire undersits beyond the 100,000 most-frequent English words, in the long tail of technical, archaic, or otherwise rare vocabulary where spelling doubt tends to strike hardest.

Beyond rank #100,000. Source: FrequencyWords open word-frequency list.

Rare enough to double-check

light a fire under is uncommon English outside the top frequency list, classed as averb. Rarity is why readers land here mid-draft. Gloss: "To motivate or encourage (someone) to start sooner or move faster.".

light a fire under doesn't appear in our generated misspelling index, typically a sign the spelling maps closely to how the word sounds. Our dataset records no confusable match here, since nothing in our dataset looks or sounds close enough to cause mix-ups.

Etymologically, the entry records: Referring to a time when, if chimney sweeps were afraid to ascend a chimney, the fire would be lit under them in order to motivate them to climb to the top. The correct English form is light a fire under, spelled L-I-G-H-T- -A- -F-I-R-E- -U-N-D-E-R.

Definition

  1. 1
    To motivate or encourage (someone) to start sooner or move faster.

Recorded use

Wiktionary example

These source excerpts show how light a fire under appears in context. They illustrate usage; the definition above remains the entry’s reference meaning.

  1. Let me see if I can light a fire under the waiter to get our order sooner.

Etymology

Referring to a time when, if chimney sweeps were afraid to ascend a chimney, the fire would be lit under them in order to motivate them to climb to the top.

Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA). See the methodology for how each field is sourced and updated.

Frequently Asked Questions

How do you spell "light a fire under"?
"light a fire under" is spelled L-I-G-H-T- -A- -F-I-R-E- -U-N-D-E-R.
What does "light a fire under" mean?
As a verb, "light a fire under" means: To motivate or encourage (someone) to start sooner or move faster.
What is the origin of the word "light a fire under"?
Referring to a time when, if chimney sweeps were afraid to ascend a chimney, the fire would be lit under them in order to motivate them to climb to the top. See the full etymology section above for more details.
Is PlainSpell free to use?
Yes, PlainSpell is a completely free word reference. You can look up definitions, pronunciations, confusable pairs, homophones, and spelling corrections across 5 languages without any sign-up or subscription.

Source: Wiktionary (via kaikki.org) Structured Wiktionary extract

Source: FrequencyWords open word-frequency list