Definition of je ne sais quoi in English:

je ne sais quoi

noun

  • A quality that cannot be described or named easily.

    ‘that je ne sais quoi which makes a professional’
    • ‘Whatever the reason, I don't seem to possess that ‘je ne sais quoi’ quite simply because I really don't know what it is.’
    • ‘Bacon, Galileo and Descartes rejected the preternatural je ne sais quoi in favour of a scientific examination of nature.’
    • ‘Parisian store owners know that their certain je ne sais quoi has more to do with quality than quoi.’

Origin

French, literally ‘I do not know what’.

Pronunciation

je ne sais quoi

/ˌʒə nə seɪ ˈkwɑː//ʒən sɛ kwa/