Seal Script of 木 -
Seal Script of 片 -
And if we check the Seal Script of 床, we will have:
Evolution history of 床：(image get from http://www.vividict.com)
|Learn one Chinese Character a day - 床|
Now it is very clear that 床 - is left half of the wood after being cut into two pieces. If you recall the Oracle Script of 片, you will realize that is 片 as well. I guess after Chinese ancestors eventually invented a furniture for sitting or lying on, looked like such furniture, thus Chinese ancestors eventually borrowed to mean it.
床 - in ancient China, it was used to mean both Chair or Bed. As time passed, 床 is used to mean Bed only, for eventually there were dedicated furnitures for siting and sleeping separately. Thus another Chinese character 椅 was created to mean Chair only. From here we also know that Chinese ancestors already had wooden furnitures during Oracle Script period.
|A typical 床 in ancient China|
床 is later extended to mean something big and flat, like river bed, exactly the same idea as English.
During Seal Script period, there was already another variation created - by adding an extra wood to emphasize 床 is created with wood.
During Clerical Script period, had its part transformed to that we had the new form . Current way of writing 床 is the continuation of .
Now let us enjoy a Chinese calligraphy with 床 inside: