Where does “cinquaenta” come from?

cinquaenta (Old Spanish) comes from Latin quīnquāgintā, from Proto-Indo-European penkʷēḱomt, from Proto-Indo-European *pénkʷedḱomt.

Ancestry of “cinquaenta”, step by step

Step	Language	Word	Meaning
1	Latin	quīnquāgintā	—
2	Proto-Indo-European	penkʷēḱomt	—
3	Proto-Indo-European	*pénkʷedḱomt	—

cinquaenta — Etymology, Origin & Word History | Etymology Explorer