business partner; partner company
Refers to a company or organization with which one has a business alliance or partnership. Often used in formal business contexts.
Our company is looking for a new business partner.
We plan to renew the contract with our partner company.
協力会社 is a cooperating company, often used for subcontractors or firms that assist in projects. 提携先 emphasizes a strategic partnership rather than just cooperation.
Compound of 提携 (ていけい, 'partnership, alliance') and 先 (さき, 'destination, counterpart'). The suffix 先 here indicates the other party in a relationship.