How do I find the relevant command for something in linux?

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http://unix.stackexchange.com – For example, say I'm trying to find the command that displays the routing table (like route) or to run a traceroute, but I don't actually know the commands that accomplish this. My understanding is that I should be able to use man -k [word], but it never seems to work: if I do man -k route on Scientific Linux 6.1, I get no results, even though I would expect it to return anything that includes the word "route" in it! Unfortunately, when I search for the answer to this, it's confounded by people explaining the find command for a file search. Thank you! (HowTos)