If "broad" refers to width:
* Narrow
* Thin
* Slender
* Tight
If "broad" refers to scope or range:
* Narrow
* Limited
* Specific
* Restricted
If "broad" refers to a general idea or statement:
* Specific
* Detailed
* Precise
If "broad" is used in a slang sense meaning "woman":
* Man
* Guy
* Fellow
So, to give you the best opposite word, I need more context!