1. The quality or state of being effective; the ability to produce a desired or intended result.
Usage: Often used in technical, military, or business contexts.; Less common than 'effectiveness' in everyday English.
2. The date on which something becomes effective or operational.
Usage: Chiefly used in legal, contractual, and administrative contexts.

Examples

• The effectivity of the new drug was demonstrated in clinical trials.
• The policy's effectivity depends on proper enforcement and public cooperation.
• The contract's effectivity begins on January 1st.
• Military strategists measure the effectivity of their operations by mission success rates.
• The effectivity of the marketing campaign was measured by sales growth.
• The law's effectivity was delayed pending regulatory approval.