Lassitude comes from the Latin words lassus and lassitudo, meaning “weary.” Our English spelling comes from the French word that developed directly from Latin, borrowed in the 15th century. 

The word "lassitude" was first used in the English language in the mid-1500s. The earliest known use of the word is in the writing of Thomas Elyot, a humanist and diplomat, in 1541.  

Here are some examples of lassitude in a sentence:

Just the facts:

Lassitude Definition & Meaning - Merriam-Webster