# Barlow

/ˈbɑɹˌɫoʊ/ (US)

Source: https://englishreference.com/word/barlow
Updated: 2026-08-15

## Senses

### 1. astronomy lens

noun · CEFR C2 · Technical

a special lens you put in a telescope to increase the magnification and see objects larger.

For teachers: a Barlow lens; a diverging lens used in series with other optics to increase the effective focal length of an optical system.

- He used a 2x Barlow to get a closer look at the craters on the moon.
- By inserting a high-quality Barlow into the optical train, the astrophotographer effectively doubled the magnification without needing to swap the primary eyepiece.

Usage: Often used as a modifier before 'lens', though frequently shortened to just 'a Barlow' in amateur astronomy circles.

### 2. pocket knife

noun · CEFR C2 · Archaic

a traditional type of folding knife with a long metal part at the handle and one or two blades.

For teachers: a type of sturdy pocket knife characterized by a long bolster and one or two blades, originally manufactured in Sheffield.

- The old man pulled a Barlow from his pocket to whittle a piece of wood.
- The collector prized the vintage Barlow for its bone handle and the distinctive elongated bolster that defined the Sheffield pattern.

Teaching tip: This term is largely historical or specific to knife collectors; most modern speakers would simply say 'pocket knife'.

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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.