Not able to be obtained, acquired or reached.(adjective)
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Use "unobtainable" in a sentence
"The point he was making was that imagination plays a greater part in sexual temptation than flagrantly exposed flesh: the apparently unobtainable is more enticing than what is freely proffered."
"Manuscripts described as unobtainable by collectors may be found together with more ordinary books."
"[Aurora - the term originated based on the word "unobtainable", because that is the prerequisite characteristic of an element that is being discussed by scientists when that element is still only hypothetical ... becasue it has never been "obtained" yet.]"