keratinocyte. [kerat′inōsīt′]. Etymology: Gk, keras + kytos, cell. an epidermal cell that synthesizes keratin and other proteins and sterols. These cells constitute 95% of the epidermis, being formed from undifferentiated, or basal, cells at the dermal-epidermal junction.tymology: Gk, keras + kytos, cell. an epidermal cell that synthesizes keratin and other proteins and sterols. These cells constitute 95% of the epidermis, being formed from undifferentiated, or basal, cells at the dermal-epidermal junction.