Sen-Senpai Share definition Flag Noun. 1. The seniority of all seniors 2. The highest role in a hierarchy system Michael is the sen-senpai of slowman. He knows everything about the company. Sen-Senpai by stupidly genius January 27, 2016 0 0 Get merch Get the Sen-Senpai mug. Buy Now — $32.95 See more merch