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’
    • ‘Parisian store owners know that their certain je ne sais quoi has more to do with quality than quoi.’
    • ‘Bacon, Galileo and Descartes rejected the preternatural je ne sais quoi in favour of a scientific examination of nature.’
    • ‘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.’

Origin

French, literally ‘I do not know what’.

Pronunciation

je ne sais quoi

/ʒən sɛ kwa//ˌʒə nə seɪ ˈkwɑː/