infill vs infirm, What's the Difference?

Which to use

“infill” is a verb and “infirm” is an adjective - they look or sound alike but fill different roles in a sentence.

#48,290
“infill” frequency rank: #46,546
“infirm” frequency rank: 94836
confusion score

Side-by-Side Comparison

Feature	infill	infirm
Definition	To fill in a space, hole or gap.	Weak or ill, not in good health.

Where the spellings diverge

Shared letters are muted; the letters that actually set infill and infirm apart are highlighted. They share 4 letters in sequence, which is exactly why the eye skips the difference.

6 ch

infill

6 ch

infirm

Spelling & Dictionary Insight

Our dataset has no pronunciation recorded for both members, so the reliable separator here is grammatical: infill is averb and infirmanadjective. On the page they share most of their letters but differ in 2 positions. Our composite confusion score for this pair is 94836, derived from the frequency rank of both members and their visual similarity.

infill is recorded at frequency rank #48,290, classified as averb. infirm is at rank #46,546, tagged as anadj, pronounced /ɪnˈfɜːm/.

Glosses for this pair are partially populated in our dataset, but the full side-by-side definitions above should still guide you to the right choice.

With a confusion score of 94836, this pair ranks #1,215 of 530,003 scored English confusable pairs - among the most confusable pairs.

Orthographic DNA of infill vs infirm

Shared letters: fin. Private to "infill": l. Private to "infirm": mr.

"infill" · 6 letters · shape VCCVCC · "infirm" · 6 letters · shape VCCVCC

Known mistypes of this pair

infill ← ifnill · inffill · infil · inflil · inifll · innfill · nifill
infirm ← ifnirm · inffirm · infimr · infirmm · infirrm · infrim · inifrm · innfirm

Frequency comparison

infill#48,290

infirm#46,546

Source: FrequencyWords open word-frequency list

Frequently Asked Questions

Can "infill" and "infirm" be used interchangeably?

No - they are not even the same part of speech. "infill" is a verb and "infirm" an adjective, so a sentence built for one is usually ungrammatical with the other.

Which is more common, "infill" or "infirm"?

"infirm" is the more common of the two: it sits at frequency rank #46,546 in our English list, against #48,290 for "infill". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

Remembering infill vs infirm

The fastest way to pick the right one every time.

Check the role first: if you need a verb, it's “infill”; for an adjective, it's “infirm”.
See each word in full, definition, IPA, etymology and its other confusables. Full “infill” entry
Browse more pairs most likely to be confused. Most confusable