apropos [keyword]

[kmurray@radon ~]$ apropos Package
rpm (8) – Red Hat Package Manager
rpm2cpio (8) – Converts Red Hat Package (RPM) to cpio archive
…

and

man [manpage]

[kmurray@radon ~]$ man rpm
Name
rpm – RPM Package Manager

Synopsis

Querying and Verifying Packages:
rpm {-q|–query} [select-options] [query-options]
rpm {-V|–verify} [select-options] [verify-options]
rpm –import PUBKEY …
…