Artificial intelligent assistant

fern-seed

ˈfern-seed
  The ‘seed’ of the fern. Before the mode of reproduction of ferns was understood, they were popularly supposed to produce an invisible seed, which was capable of communicating its invisibility to any person who possessed it.

1596 Shakes. 1 Hen. IV, ii. i. 96 We haue the receit of Fern-seede, we walke inuisible. 1630 B. Jonson New Inn i. Wks. (Rtldg.) 411/1, I had No med'cine, sir, to go invisible; No fern-seed in my pocket. 1756 Smart Horat. Canons Friendsh. 76 Ask thy heart, if Custom..Hath sown no undiscover'd fern-seed there. 1815 Scott Guy M. xlv, ‘They say she has gathered the fern-seed and can gang ony gate she likes.’ 1859 Sala Tw. round Clock (1861) 266 We..are in the receipt of fern-seed, and can walk invisible.

Oxford English Dictionary

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