kivuton
When we talk about something being without pain or painless, we use the word kivuton. This adjective is formed from the noun kipu, which means 'pain', and the suffix -ton, which indicates 'without'. So, literally, kivuton means 'without pain'.
You can use it to describe a procedure that doesn't cause pain, like 'kivuton toimenpide' (a painless procedure), or to talk about a feeling of relief, such as 'olo on kivuton' (the feeling is painless/one feels painless).