# SID

/ˈsɪd/ (US)

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

## Senses

### 1. aviation departure route

noun · CEFR C1 · Technical

Stands for Standard Instrument Departure. It is a specific path a pilot must follow when taking off from an airport.

For teachers: Abbreviation for Standard Instrument Departure. A published flight procedure followed by aircraft immediately after takeoff to ensure a smooth transition to the en route phase.

- The pilot checked the SID for the airport to make sure he followed the correct path after takeoff.
- Air traffic control cleared the flight for the OCKHAM SID, requiring the pilot to maintain a specific climb gradient until reaching the first waypoint.

Usage: Usually used with the definite article 'the' in aviation contexts.

### 2. computing security code

noun · CEFR C2 · Technical

Stands for Security Identifier. It is a unique code that a computer system uses to identify a user or a group.

For teachers: Abbreviation for Security Identifier. A unique, variable-length character string used to identify a trustee, such as a user account or group, within a Windows environment.

- The system administrator checked the user's SID to fix the permission error.
- When a user account is deleted and recreated with the same name, it receives a new SID, preventing it from inheriting the old account's permissions.

### 3. vintage sound chip

noun · CEFR C2 · Technical

Stands for Sound Interface Device. It was a famous chip in old Commodore 64 computers that made unique electronic music.

For teachers: Abbreviation for Sound Interface Device. A programmable sound generator chip used in the Commodore 64 and Commodore 128 home computers, noted for its distinctive synthesis capabilities.

- Many modern musicians still use the SID chip to get that classic 8-bit sound.
- The SID chip's three independent oscillators and multi-mode filter allowed for complex textures that were unprecedented in early 1980s home computing.

### 4. once a day

adverb · CEFR C2 · Technical · Formal

A term used by doctors or vets meaning to take a medicine once every day.

For teachers: Abbreviation for 'semel in die'. A medical instruction indicating that a medication should be administered once daily.

- The vet told me to give the cat her pill SID, so I do it every morning.
- The prescription was marked SID, instructing the patient to take the dosage at the same time each evening to maintain consistent blood levels.

Usage: Typically written in lowercase (s.i.d.) on prescriptions, though often capitalized in clinical notes.

### 5. a person's name

noun · CEFR A2 · Informal

A short, friendly name for a man named Sidney or Siddhartha.

For teachers: A hypocorism or diminutive form of the masculine given names Sidney, Siddhartha, or occasionally Sydney.

- My neighbor Sid has lived in this street for over forty years.
- Sid was a common nickname in mid-century Britain, though its popularity as a standalone name has fluctuated significantly since then.

## Examples

- The pilot followed the SID to climb away from the busy airport.
- Air traffic control assigned the pilot a specific SID to ensure the aircraft avoided the nearby mountain range during departure.
- Modern flight management systems allow pilots to program the assigned SID directly into the computer, automating the complex turns and altitude restrictions required during a heavy-traffic departure.

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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.