This is the 3585th most frequent Chinese word.
烈
Fierce; intense; strong.
In this sentence, '烈' is used to describe the intensity or strength of sunlight.
太阳的光芒十分强烈。
The sunlight is very intense.
Here, '烈' is used in '烈性' to mean strong or intense character and determination.
战士们的烈性令人敬佩。
The fighters' fiery temperament is commendable.
In this context, '烈' describes the forceful nature of combustion.