Old English cennan 'tell, make known', of Germanic origin; related to Dutch and German kennen 'know, be acquainted with', from an Indo-European root shared by can¹ and know. Current senses of the verb date from Middle English; the noun from the mid 16th century.

• know from Old English:

  The ancient root of know is shared by can and ken, ‘to know’ in Scots (all Old English), and also by Latin noscere, and Greek gignōskein ‘to know’, source of words such as agnostic. To know in the biblical sense, meaning ‘to have sex with’, comes from biblical uses such as the verse in the book of Genesis: ‘And Adam knew Eve his wife; and she conceived, and bare Cain.’ To know the ropes is to be thoroughly acquainted with the way in which something is done. The phrase comes from the days of sailing ships, when skill in handling ropes was essential for any sailor—an alternative is know their onions. The ancients valued self-knowledge as the way to wisdom—inscribed on the Greek temple of Apollo at Delphi were the words know thyself. The line ‘ It's life, Jim, but not as we know it’ is the mainstay of anyone trying to do an impression of Dr Spock from the TV series Star Trek, but he never said it in the programme. He did say that there was ‘no life as we know it’, but the quoted phrase is from the 1987 song ‘Star Trekkin'’ by the Firm. See also gnome