“Leggiero” and “Pesante”
Italian “score sheet poetry” that extensively describes the desired feelings of tempo changes or interpretation is rather uncommon in the scoring session world. Most of the time, the tempo is fixed through a click track and in order to describe desired playing attitudes, English terms have become more common. Generally, stay within reason with lengthy verbal description. Talking to the orchestra describing the scene before the take might be more helpful than cluttering the pages with text.
However, the words leggiero (easy, lightly) and pesante (heavy, strong) are quite common and indeed quite helpful to define playing attitude. They will for instance make a difference whether a row of staccato notes needs to be played with a lighthearted, bouncy attitude or as threatening ominous and epic. A conscious and clever use of these words will most likely save you from needing to address the interpretation of such a passage after a first take.