soporific.

1. Causing or tending to cause sleepiness, literally or through dullness.

2. A substance or remedy that causes or promotes sleep.

Use it for

Words that belong together

• a soporific effect
• a soporific lecture

On the page

The soporific rhythm of the lecture blurred her notes into a single line.

Warmth and the train’s steady motion had a soporific effect after the sleepless night.

Usage notes

Primary category: literary. Forms: Comparative more soporific; superlative most soporific where gradation is meaningful. Noun singular soporific; plural soporifics. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.