គ្រូ (Khmer) comes from Old Khmer គុរុ, from Sanskrit गुरु, from Proto-Indo-Aryan gr̥Húṣ, from Proto-Indo-Iranian gr̥Húš, from Proto-Indo-European gʷréh₂us, from Proto-Indo-European -us — Forms adjectives from Caland system roots.
គ្រូ (Khmer): teacher