at first Definition

first
adj

1. In counting: before all others; before the second and following ones.
2. Earliest in time or order; the starting object of a series of objects.

Thesaurus: initial, original, leading, head, opening, introductory.
3a. The first day of the month;

Form: the first
3b. golf.
The first hole.
Form: the first
4. The most important; foremost in importance.

Example: first prize
Thesaurus: uppermost, primary, principal, paramount, highest.
5. Basic; fundamental.

Example: first principles
6a. music.
Having the higher part;
Example: the first violins
6b. music.
Being the principal player.
Example: the first clarinet

adverb

1. Before anything or anyone else.

Thesaurus: in the beginning, at the outset, early on, to start with, to begin with, before all else, originally, beforehand, initially.
2. Foremost.

Example: got in feet first
3. Before doing anything else.

Example: first make sure of the facts
4. For the first time.

Example: since he first saw him
5. Preferably; rather.

Example: I'd die first
6. Firstly.

noun

1. A person or thing coming first, eg in a race or exam.
2. colloq
A first occurrence of something; something never done before
Example: That's a first for me!
3. The beginning; the start.

Example: from first to last
4. Denoting the first or lowest forward gear (sense 2) in a motor vehicle.

Example: She changed from first to second
(chiefly Brit)
5. education.
First-class honours in a university degree; a degree of the highest class.
Form: a first

Idiom: at first

At the start of something; early on in the course of something.

Idiom: at first hand

Directly from the original source.
Example: to obtain information at first hand

Idiom: first and last

Essentially; on the whole.

Idiom: first come, first served

Those who respond before others to an offer have priority over them.

Idiom: first thing

colloq
Early; before anything else; as the first action of the day.
Example: I'll do it first thing in the morning

Idiom: first things first

An expression suggesting that one should organize oneself by doing the most important things before other things.

Idiom: get to first base (make first base)

To complete the first stage of a process.

Idiom: in the first place

From the start; to begin with.
Example: He didn't want to go in the first place

Idiom: not have the first idea about something (not know the first thing about something)

colloq
To be completely ignorant about it; to know nothing about it.

Etymology: Anglo-Saxon fyrest.