# clag up

CEFR C1 · Phrasal verb

Source: https://englishreference.com/word/clag-up
Updated: 2026-04-24

## Definition

to become blocked or stuck with something thick and sticky so that a machine or system stops working well.

For teachers: to become obstructed or congested by a sticky or viscous substance; often used in mechanical or metaphorical contexts to describe a loss of efficiency.

## Examples

- The printer keeps clagging up because of the cheap ink.
- If you don't clean the filter regularly, it will clag up with dust and grease.
- The gears began to clag up as the lubricant thickened in the freezing temperatures, eventually bringing the entire assembly to a halt.

## Pitfalls

- Not "The pipe clagged." but "The pipe clagged up." — the particle 'up' is necessary to complete the meaning of becoming fully blocked.

## Usage notes

- often used with the preposition 'with' to name the substance causing the blockage.
- Teaching tip: this is a more informal and vivid alternative to 'clog up' or 'block'; it is particularly common in British English and technical hobbyist circles.

---

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.