1. bottom; sole; bed (of a river)
この大きさなら底の部分は大丈夫だな。At this size, the bottom part should be fine.
2. depths (e.g. of despair, the sea); bottom (of one's heart); the heart (of something)
今この国は、深い悲しみの底に沈んでいる。This country is now sunk in the depths of deep sorrow.
3. limit; end; extremities; bounds
つまり彼は底が知れないってヤツだね！In other words, there's no telling where his limits are!
4. bottom (e.g. of share price); bottom price