a branch of mathematics in which letters are used to represent numbers in solving for unknown variables
You need to know basic math skills before you can enroll in an algebra class.

to tell people about something officially
The National Weather Service will announce that there is a possibility of a tornado.

either of the two upper chambers on each side of the heart that receive blood from the veins and in turn force it into the ventricles.
Inside the building there is a huge sculpture in the atrium.

a period of time when something or someone stops an activity before continuing again later
Let's take a break for a few hours.

a series of items, written, stated , or memorized in order
I made a list of toys I wanted for Christmas.

watch something attentively
Tony observed the class before beginning the lesson.

to take part in an activity or event with others
I really encourage you to participate in this item donation event.

to listen closely and focus
The students were not paying attention to the teacher.

to formally agree in writing to participate in something
Let's sign up for the volleyball team.

the Sun, Earth, eight other planets, moons, comets, that move around the sun
The solar system that we live in is called the Milky Way.