Search the whatis database for strings.
Syntax
apropos keyword ...
The whatis database is a set of database files containing short descriptions of system commands for keywords. apropos searches this database and displays the result on standard output.
Examples
List all the man(1) and man(8) commands
$ apropos ' ' | egrep '\(1\)|\(8\)'
“A man travels the world in search of what he needs and returns home to find it” - George Moore
Related macOS commands:
whatis - search the whatis database for complete words.