To a search engine, "house", and "boat" are different than "house boat".
To be honest though keywords this day and age are almost completely useless, so I wouldn't waste your time. Spend your time on the meta description, title tag (page title), key-word density in your body, and your header tags (H1, H2, etc).
If you are referring to keywords in Metatags, Google does not use them in it's ranking.
In Google's webmaster guidelines, keywords barely rate a mention
and Google has stated that its spiders and bots ignore them
As the others have said, spend your time on good, rich content (especially text) in your page since keywords in <meta> tags are more or less ignored by search engines these days.
This is GREAT stuff. I've been scratching my head over search engines for a while and this really helps.
Thanks a million and all the best.