If booking is a generic term, then so is apple, so is amazon...
This is another common domainer misconception about trademarks. Trademarks are not monopolies in the trademark terms. It is useful to think of a trademark as having two parts:
(a) the term itself
PLUS (b) the goods or services for which it is a trademark.
In other words, when someone say "X is a trademark", you should ask yourself what is it a trademark
for.
The word "apple" is a generic word for apples. The trademark "apple" is a trademark for computers, music services, and the other various goods and services of the well-known computer company.
The word "tide" is a generic word for what the gravity of the moon and sun do to the sea. The trademark "tide" is a trademark for laundry detergent.
The point that cipcip is missing is that you cannot get a trademark for "apple" to sell apples.
You cannot get a trademark for "bud" to sell flowers. You can get a trademark for "bud" to sell beer.
Now, there is an additional layer of considerations when we are talking about marks that are famous or inherently distinctive. A famous mark would be, for example, Coca-Cola. If you were to use Coca-Cola as a brand for, say, shoes, then you would have a problem. That mark is so well known that its use on just about anything would probably be understood by consumers as having originated with the soft drink maker. Similarly, inherently distinctive marks, such as made-up word like XEROX, have no other meaning than as a reference to the goods or services of that company.