To admit the existence or truth of: The doctors acknowledged that the treatment had not been successful. To express recognition of; make notice of:"When he saw me acknowledge him, he smiled as if we were dear friends"(Angela Patrinos). To express gratitude or appreciation for or to: acknowledged the contributions of the volunteers; acknowledged her editor in the preface to the book. To report the receipt of (something) to the sender or giver: acknowledge a letter. Law To accept or certify as legally binding: acknowledge a deed of ownership.