The i is substituted for the final a of gandha at the end of a bahuvrīhi samāsa when gandha means 'a little'.,
Thus सूपोऽल्पोऽस्मिन् = सूपगन्धि भोजनम् \food with a little broth\. So घृतगन्धि \food with a little-a mere scent- of ghee\. So क्षीरगन्धि ॥ Here गन्ध is a synonym of अल्प ॥,