Heartily means doing something with genuine enthusiasm, energy, or sincerity. When you laugh heartily at a friend's joke, you're genuinely cracking up because you find it truly funny. When someone agrees heartily with an idea, they're supporting it with real conviction and passion. When guests eat heartily at dinner, they're digging in with real appetite and enjoyment.

The word comes from heart, suggesting something done with your whole heart rather than half-heartedly or reluctantly. If you throw yourself heartily into a science project, you're working with real passion and commitment. If you greet someone heartily, you're giving them a warm, genuine welcome, not just a quick “hey” while looking at your phone.

Notice how heartily captures both the feeling inside (enthusiasm, sincerity) and how it shows on the outside (energy, warmth). When an author writes “she thanked them heartily,” readers understand this wasn't just a mumbled “thanks” but a sincere expression of gratitude. The word adds life and authenticity to the action it describes.