# shim

/ˈʃɪm/ (US) · /ʃˈɪm/ (UK)

Source: https://englishreference.com/word/shim
Updated: 2026-08-27

## Senses

### 1. mechanical spacer

noun · CEFR C1 · Technical

a thin piece of wood, metal, or plastic used to fill a small gap or make something level.

For teachers: a thin, often tapered piece of material used to fill small gaps, provide support, or ensure precise alignment between components.

- The carpenter used a small wooden shim to stop the table from wobbling on the uneven floor.
- The technician inserted a stainless steel shim to achieve the precise clearance required for the high-speed turbine assembly.

### 2. computing compatibility layer

noun · CEFR C1 · Technical

a small piece of software that helps an old program run on a new system by fixing compatibility issues.

For teachers: a small library that transparently intercepts API calls and changes the arguments or handles the operation itself to provide compatibility.

- We had to install a shim so the old database software could talk to the new operating system.
- The developers implemented a polyfill shim to ensure that modern JavaScript features would function correctly in legacy web browsers.

### 3. to level or align

verb · CEFR C1 · Technical

to use thin pieces of material to make something level or fit perfectly.

For teachers: to adjust, level, or align a mechanical assembly by the insertion of shims.

- You might need to shim the door frame if the wall isn't perfectly straight.
- The installation crew spent hours shimming the heavy machinery to ensure it was perfectly level before bolting it to the concrete pad.

Usage: Often used as a transitive verb taking the object being leveled.

### 4. fraudulent device

noun · CEFR C2 · Technical

a very thin device that criminals hide inside a credit card reader to steal information.

For teachers: a paper-thin electronic device inserted into a card-reading slot to intercept data from the chip of a credit or debit card.

- The bank warned customers to check the ATM for a shim before inserting their cards.
- Unlike bulky skimmers, a shim is thin enough to reside entirely inside the card slot, making it nearly impossible for a casual user to detect.

## Examples

- The mechanic used a metal shim to level the wheel.
- To fix the wobbly table, the carpenter inserted a wooden shim between the leg and the floor.
- The developer created a compatibility shim to allow the legacy application to communicate with the new cloud-based API without requiring a complete rewrite of the source code.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.