This is an irregular feature - both in frequency and oddness - dedicated to a word I came across that I have never previously used.
sfumato (sfoo-MAH-toe) n. An artistic technique of blurring or softening of sharp outlines by the gradual blending of tones; using outlines, colors, and shading in such a way as to give a misty appearance.
Sfumato is most recently of Italian origin, formed from the past participle of sfumare ("to evaporate" or "to fade out"). Sharp-eyed readers will also recognize the Latin fumare ("to smoke"), which can also be found in the equivalent Spanish verb fumar.
Leonardo da Vinci's Mona Lisa is noted for its innovative use of sfumato techniques, and da Vinci is often credited for bringing the term into widespread use.