בַּעֲדִינוּת
The Hebrew word for gentle is עדין in the masculine and עדינה in the feminine. You may know people by these names – Adin and Adina.
These words derive from עדן – Eden, as in the Garden of Eden (עדן-Eden is also a beautiful name), since gentleness is a virtue of Edenic proportion.
Gently is בעדינות, as in:
אבי, תרים את הקופסה בעדינות – יש בה דברים שבירים.
Avi, pick up the box gently – there are fragile items (things) in it.