Although you can have multiple keywords assigned to a campaign, a keyword can only be assigned to one campaign at a time. You cannot use the same keyword in multiple campaigns at the same time.
To 'transfer' a keyword from one campaign to another, you will first need to un-assign the keyword from the campaign it is assigned to.
1 - Navigate to the Campaign Builder of your campaign
2 - Click the action button to the right of your keyword received goal
3 - Click UnAssign Keyword