Legal Question in Business Law in California

It depends on a factual analysis. You are not allowed to use a name that is confusingly similar to an existing name. If you are doing auto repair with the name, and someone else is using it to sell software, you may be ok. What are your using it for? What is the trademark holder using it for. Is this a tradeneme ( used for yoru business) or is this a label attached to a product? You really need to ask a patent and trademark counsel to assist. It can be very expensive to start an business then find another company has the right to the name, and can force you to stop it's use.

I'd like to expand upon and possibly clarify the previous answer. Trademarks are registered for classes of business, not everyone with the same or similar name......... for example, the name "Purple Passion" could legally be assigned to and used by a clothing manufacturer, a brand of lipstick, and a vintner for its Zinfandel. If the existing business "Cloudcast" is in the weather forecasting business, for example, and you intend to be in the art studio business, the trademark office would almost certainly issue you a trademark for your proposed name. I do agree, however, that you should use an intellectual-property attorney at an early stage to prepare and file a trademark application for your name and in your business category. It might also be worthwhile to inquire of the other company whether it sees your proposed name as legally infringing, and if so, why. You'll probably get a favorable response, but checking in is worth the effort.