How to check if a string is in the english dictionary?

Is there some way to reference an english dictionary and check if a string is in it?

Mac:

$ grep --color=always "gopher" /usr/share/dict/words

Ubuntu Linux:
$ sudo apt-get install --reinstall wamerican
$ grep --color=always "gopher" /usr/share/dict/words

Know about windows too by any chance ;)?

What's windows?

I think its some kind of spyware?