The term "eldest hand" refers to the person in a group with the most experience or seniority. There are several synonyms for this phrase, such as "most veteran," "senior colleague," "most seasoned," "most knowledgeable," "most experienced member," and "most senior member." These terms are often used in a professional setting, such as in a workplace or a team environment. They indicate respect and recognition for the person who has been in their role for the longest period of time and has the most expertise. Using these synonyms can help to convey appreciation and acknowledgement of the value that the eldest hand brings to the team.