lighthearted
adj.having a cheerful and friendly attitude. You use this to describe someone who is not serious or someone who makes others feel relaxed.
adj.characterised by a cheerful, friendly, and easygoing nature. Often used to describe a person's disposition or the tone of a conversation.
“He has a lighthearted way of looking at life.”
“The meeting started with a lighthearted game to help everyone relax before discussing the serious budget issues.”
“Despite the gravity of the situation, the manager maintained a lighthearted tone to prevent the team from becoming overly anxious about the upcoming merger.”
From Middle English lyght hertyd, liȝt-hertid, from light (adjective) + herted, hertid (“having a disposition”, adjective) (equivalent to light + hearted), from the noun herte. See more at light, heart, -ed.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.