Grand-pappy is a term of endearment used for someone's grandfather or an elderly man. However, if you're looking for other synonyms to use, there are a few options. For example, you could use pop-pop, papa, grandad, grandpa, gramps, or even old-timer. While these all convey a similar sentiment, the tone and connotation of each word may differ slightly. Pop-pop or papa may be more casual and affectionate, while grandad or grandpa may be more traditional and respectful. Gramps may convey a sense of familiarity and fondness, while old-timer may suggest a deep sense of respect and wisdom. Ultimately, the choice of synonym will depend on your relationship with the person and the tone you want to convey.