can i use one domain name for multiple forms

probably not

Do you mean to use a custom domain with your forms? If so, you may setup custom domain by adding a DNS record. Please refer to the guide below that can assist you with using custom domains.

http://www.jotform.com/help/144-How-to-use-Custom-Domains-with-Jotform

If you are referring to something different or need any further assistance, please let us know. We will be happy to assist.