Where does “पक्षिरूप” come from?

पक्षिरूप (Sanskrit) comes from Sanskrit पक्षिन्, from Sanskrit -इन्, from Proto-Indo-European -iHnos, from Proto-Indo-European -no- — adjectival suffix.

Ancestry of “पक्षिरूप”, step by step

पक्षिरूप traces back through two separate lines of ancestry.

via Sanskrit पक्षिन्

Step	Language	Word	Meaning
1	Sanskrit	पक्षिन्	bird
2	Sanskrit	-इन्	possessing, showing possession, doer
3	Proto-Indo-European	-iHnos	Creates adjectives of materials
4	Proto-Indo-European	-no-	adjectival suffix

via Sanskrit रूप

Step	Language	Word	Meaning
1	Sanskrit	रूप	outward appearance, color, form, shape; right...
2	Sanskrit	रूप्	to form, shape

Words derived from “पक्षिरूप”

पाखिरूं
पखेरू
पाखरू
फुलपाखरू

Every word from Proto-Indo-European -no- →Every word from Sanskrit -इन् →Every word from Sanskrit पक्षिन् →