The option that can be used as a one-word substitute for the given group of words "The act of washing oneself" is "Ablutions."

Explanation of the options:

☀ Ablutions: Ablutions refer to the act of washing oneself, typically in a religious or ceremonial context.

☀ Solutions: Solutions refer to answers or remedies to problems or challenges.

☀ Steaming: Steaming refers to the process of exposing something to steam, often used in cooking or for therapeutic purposes.

☀ Bathing: Bathing refers to the act of washing oneself, typically in water for personal hygiene or relaxation purposes.