If something is broad, it’s wide. The word "broad" is an adjective.
The roads in this city are very broad.
A sidewalk should be broad enough for two people to walk side by side.
Our teacher has a broad knowledge of American literature.
Doctors have a broad understanding of how the human body functions.
Broad shoulders make a man or a woman look more powerful.
A broad smile spread across the woman’s face when she learned she was the winner of the contest.
A man had his car stolen in broad daylight. (broad daylight = during the day as opposed to night)
He had his shoulders measured because he wanted to know how broad they were.
The word "broaden" is a verb.
simple
past
past participle
broaden
broadened
broadened
Traveling is a good way to broaden your knowledge of the world.
You can broaden your horizons by going to college. (broaden one’s horizons = to be exposed to new ways of thinking)
Working with elderly people can broaden your horizons.
The highway was broadened in order to accommodate more cars. (The highway was made wider.)
The word "broad" is found in some compound nouns:
A live radio or television broadcast can capture the attention of millions of people.
Broadway is an area of New York City where theater goers can watch live theatrical productions.
Many American cities have a street named Broadway.
Broadband internet provides fast downloads and uploads.
The broad jump is an athletic event in which a person jumps to achieve a long distance.
A dandelion is a broadleaf weed.
Note: The word "broad" is also a derogatory term for a woman. It’s use is out of fashion, but you might hear it used if you ever watch old American movies: She’s a very smart broad.
He had his shoulders measured because he wanted to know how broad they were.