Definition of unobtainium in US English:

unobtainium

(also unobtanium)

noun

informal
  • A highly desirable material that is hypothetical, scientifically impossible, extremely rare, costly, or fictional, or has some of these properties in combination.

    ‘what type of cabling are we talking about, steel, composite, unobtainium?’
    • ‘‘It's made of carbon, aluminium, titanium,’ he revealed, before, perhaps sensing that his audience wasn't suitably impressed, adding: ‘and, er, unobtainium.’’
    • ‘But the Japanese 8mm Nambu cartridge might as well have been made of unobtainium.’
    • ‘Indeed, the claims made for this technology sometimes make it sound like the legendary aerospace material ‘unobtainium.’’
    • ‘Veteran space industry analyst John Pike, director of GlobalSecurity.org, likes to joke that the required substance should be dubbed ‘unobtainium.’’

Pronunciation

unobtainium

/ˌənəbˈtānēəm/