I have multiple OS365 accounts. I want to share my contacts across those accounts.
Yes you can share your contacts with others within your "organization/domain as well as with others outside of your organization. You must have an Office 365 or Exchange account using Outlook.
There may be ways of sharing with others that do not have this type of account, but that is not the question.
Within your organization, click the contacts folder, home, share, Share contacts, Fill out the To field, and possible check the "Request permission to view the recipients Contacts folder".
When they recieve the request they will respond.
For people outside of your organization, do the same thing, but you may receive an error saying your organization does not support this or if you receive an error from the recipient you may have to discuss the error with them or their organizations administrator. ,