“Un” is a prefix in English meaning “not.” Adding it to a word changes that word to the opposite meaning. For example, “fair” becomes “unfair.” Some “un” words describe negative behavior or character, but some describe desirable traits.

“Scientists warn that parts of southern Africa already hit by record droughts now face another potential food crisis because [of] the invasion of a crop-eating pest, known as the ‘fall armyworm’” (BBC, February 14, 2017). Experts are unsure of how this caterpillar, native to the Americas, arrived in Africa, and the pest has arrived following two years of drought. “South Africa, the region’s biggest maize producer, has confirmed the destruction of crops from the pest in six different provinces.