A Persian word in a Sinitic topolect

Yesterday afternoon at Indiana University I gave a wide-ranging lecture on Iranian and Chinese interconnections from the Bronze Age through the late imperial period.  After the lecture, Chen Su, a doctoral candidate in Central Eurasian Studies, approached me and said that some of the points I made helped her to realize something about her own speech that had confused her for years.

Chen Su, who hails from Xi'an, where Guanzhong topolect is spoken, had noticed an interesting coincidence in the similarity of the pronunciation between Persian and Guanzhong topolect for the word "head". On the one hand, we have Persian sar سر （it's the same in Middle Persian).

The corresponding Guanzhong topolectal word is sá.

The usual Mandarin words for "head" are tóu 頭 and shǒu 首.

What I find most revealing is that there is no exact character for this oral term in Guanzhong topolect.  According to Chen Su, even in modern Chinese dictionaries there is no parallel character that has the same pronunciation as this topolectal word for "head".