This is the 1144th most frequent Japanese word.
優しい
Kind; gentle.
In this sentence, "優しい" describes the teacher as being kind or gentle in their demeanor, particularly in their teaching approach.
その先生は優しいので、わからないところを丁寧に教えてくれます。
The teacher is kind, so they patiently teach unclear points.
Here, "優しい" is used to describe the voice, indicating it has a calm and soothing quality.
彼の声はとても優しいんですね。
His voice is very gentle, isn't it?
In this sentence, "優しい" is used metaphorically to describe the color tones of the paintings, suggesting they are soft and pleasing to the eyes.