To add (an ingredient) by mixing or blending.(verb)
To fit unnoticed into a surrounding.(verb)
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Use "blend in" in a sentence
"The machines also handled mind-stuff, but mechanically channeled, focused, and projected; the result was a shifting, flickering, nightmarish distortion of emanations in which Robane and his instruments seemed to blend in constantly changing patterns."
"THE BUTCHER FOUND IT EASY to blend in with the hot-shit college students on the campus of George Washington University."
"A desert creature from Earth-or from a dozen other worlds-would blend in very well with the dry country we flew over on the way here, I think."