Where does “Margashirsha” come from?

Margashirsha (English) comes from Sanskrit मार्गशीर्ष, from Pali Māgasira.

Ancestry of “Margashirsha”, step by step

Step	Language	Word	Meaning
1	Sanskrit	मार्गशीर्ष	—
2	Pali	Māgasira	—

Margashirsha — Etymology, Origin & Word History | Etymology Explorer