unpainful
/(ˌ)ʌnˈpeɪnf(ʊ)l/adjective
1Not causing or involving pain, distress, trouble, or discomfort.
2Of a feeling, emotion, condition, etc.: marked or characterized by the absence of pain or distress; not accompanied by pain or distress.
Origin
Late Middle English; earliest use found in Guy de Chauliac's Grande Chirurgie. From un- + painful.