Symbols:A

atto-

$\mathrm a$

The Système Internationale d'Unités symbol for the metric scaling prefix atto, denoting $10^{\, -18 }$, is $\mathrm { a }$.

Its $\LaTeX$ code is \mathrm {a} .

are

$\mathrm a$

The are is a measure of area:

One are is equal to a square whose side measures $10$ metres.

 $\displaystyle$  $\displaystyle 1$ are $\displaystyle$ $=$ $\displaystyle 100$ square metres $\displaystyle$ $\approx$ $\displaystyle 119 \cdot 60$ square yards

$\mathrm A$ or $\mathrm a$

The hexadecimal digit $10$.

Its $\LaTeX$ code is \mathrm A  or \mathrm a.

Celestial Altitude

$a$

Let $X$ be a point on the celestial sphere.

The (celestial) altitude of $X$ is defined as the angle subtended by the the arc of the vertical circle through $X$ between the celestial horizon and $X$ itself.

It is often denoted by $a$.

Azimuth (Astronomy)

$A$

Let $X$ be a point on the celestial sphere.

The spherical angle between the principal vertical circle and the vertical circle on which $X$ lies is the azimuth of $X$.

The azimuth is usually measured in degrees, $0 \degrees$ to $180 \degrees$ either west or east, depending on whether $X$ lies on the eastern or western hemisphere of the celestial sphere.

It is often denoted by $A$.

Alternating Group

$A_n$

Inverse

a-

Prefix indicating anti.

An abbreviation for arc, anti- or argument.

Not

a-

Prefix indicating not.

alog

Abbreviation for the antilogarithm of a general logarithm.
If no base is given, the common logarithm (that is, base $10$) is assumed.