# FIR

/ˈfɝ/ (US) · /fˈɜː/ (UK)

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

## Senses

### 1. evergreen tree

noun · CEFR B1

a tall evergreen tree with needles and cones that stays green all year.

For teachers: a coniferous evergreen tree of the genus Abies, characterized by flat needles and upright cones.

- We walked through a forest of tall fir trees covered in snow.
- The hillside was densely populated with silver fir, providing a stark green contrast against the grey granite peaks above.

### 2. wood from a fir tree

noun · CEFR B2

the wood that comes from a fir tree, often used for building.

For teachers: the timber or wood derived from fir trees, typically used in construction or paper pulp production.

- The cabin was built entirely from local fir and pine.
- The carpenter preferred working with fir for the internal framing due to its straight grain and relatively high strength-to-weight ratio.

### 3. aviation airspace

noun · CEFR C2 · Technical

Stands for Flight Information Region.

For teachers: Abbreviation for Flight Information Region; a specific volume of airspace where flight information and alerting services are provided.

- The pilot contacted the London FIR as the plane crossed the coast.
- As the aircraft transitioned between the two FIRs, the crew noted a slight discrepancy in the reported altimeter settings from the respective controllers.

Usage: Usually capitalized as FIR.

### 4. digital signal processing

adjective · CEFR C2 · Technical

Stands for Finite Impulse Response.

For teachers: Abbreviation for Finite Impulse Response; describing a filter whose response to any finite length input is of finite duration.

- The engineer used an FIR filter to clean up the audio recording.
- The system designer opted for an FIR filter to ensure linear phase characteristics, despite the higher computational cost compared to recursive alternatives.

Usage: Used as an attributive adjective, almost always capitalized.

### 5. police report

noun · CEFR C1 · Dialect · Formal

Stands for First Information Report.

For teachers: Abbreviation for First Information Report; a document prepared by police in certain countries after receiving information about a crime.

- The victim went to the police station to file an FIR after the robbery.
- The magistrate noted that the details in the FIR were inconsistent with the testimony provided by the primary witness during the preliminary hearing.

Teaching tip: This term is specific to the legal systems of South Asian countries like India, Pakistan, and Bangladesh.

## Examples

- The pilot contacted the next FIR as they crossed the border.
- As the aircraft entered the London FIR, the crew established communication with the regional controllers to receive updated weather reports.
- Oceanic FIRs cover vast areas of international waters where radar coverage may be limited, requiring pilots to provide regular position reports via high-frequency radio or satellite links.

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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.