intimate friend / close companion
Adjective/noun (faʿīl pattern). Feminine: خَلِيلَةٌ. Plural: أَخِلَّاءُ (akhillāʾ). From خُلَّةٌ (intimate friendship). The highest level of friendship.
Abraham is called Khalīl Allāh (Friend of God) - the only person given this title in the Quran, reflecting the highest human-divine relationship.