Fetching details from the dictionary...

at leisure; in a relaxed manner; in a carefree manner; quietly; peacefully
to relax; to take it easy; to chill
日曜日はのんびりと家で過ごしています。
I spend my Sundays relaxing at home.
公園でのんびり散歩を楽しんだ。
I enjoyed a leisurely walk in the park.
のんびりした性格の人が好きです。
I like people with a relaxed personality.