宵の口

1. Origins, structure, and basic meaning

• Structure: 宵の口 is read as よいのくち and is a fixed time expression for the beginning of the evening.
• Basic usage: It identifies when rain began or an early-evening period when a shop still had many customers.

2. Common pitfalls and similar expressions

• Starting point with から
  • 宵の口から makes early evening the starting point of the rainfall.
• Fixed expression
  • Do not interpret 口 as a literal mouth here; learn 宵の口 as one unit meaning early evening.