We can use whatis to get the same results we would get with man -f:
# whatis passwd
passwd (1) - update user’s authentication tokens
sslpasswd (1ssl) - compute password hashes
passwd (5) - password file
The command which shows us the full path of the given command:
# which passwd → show just the first match
/bin/passwd
.
# which -a passwd → show all the matches
/bin/passwd
/usr/bin/passwd
We can achieve the same result with the whereis command: