1. deep (colour); dark
小屋の中を、濃い金色の光が満たした。Dense golden light filled the inside of the hut.
2. strong (flavour, smell, etc.)
味が濃いとそれはそれでダメなんだよ。If the flavor is strong, that's no good either.
3. thick (consistency); dense
今日も霧が濃いですねー。The fog is thick again today, isn't it?
4. strong (possibility, etc.)
確かに考えられるとしたらその線が濃いな。True, if anything, that is the most likely possibility.
5. thick (i.e. "as thick as thieves"); close; deep (love, etc.)