Khadar
Linguistically it comes from the Arabic root خ-ض-ر meaning 'green', and it is commonly used as a personal name in Somali communities as a vernacular form; so it is Arabic in origin with attested Somali usage.
The Quran narrates the episode commonly associated with al-Khiḍr in Surah Al-Kahf (18:65-82). Classical exegesis identifies that figure with Khidr/Khadar in tradition, though the text relates the episode rather than using a universally fixed proper name in every reading.
The typical Arabic representation linked to this root is خضر (often rendered with the definite article as al-Khiḍr for the traditional figure).
Yes. It is used historically and presently in Somali and some Arabic-speaking families; it is relatively uncommon and carries nature- and tradition-linked connotations.
Khadar is primarily a masculine form. Feminine names expressing the idea of 'green' or verdure are rare as direct cognates; communities more commonly choose related nature names for girls.