General English


  • noun a small dark-grey mammal which makes tunnels under the ground and eats worms and insects
  • noun an SI unit of measurement of the amount of a substance.
  • noun the part of a mole plough that cuts a round channel underground


  • An excavation machine used to bore tunnels.


  • The SI fundamental unit of amount of substance. Such a substance may be subatomic particles, atoms, molecules, ions, and so on. There are approximately 6.022142 × 1023 elementary entities in a mole.
  • The molecular weight of a substance, expressed in grams per mole (1). For instance, a mole of sodium chloride is approximately 58.44 grams, as the combined molecular weight of sodium and chlorine is approximately 58.44 atomic mass units. Also called gram-molecular weight.


  • As mole poblano, but with added tomatoes, thickened with tortillas and sweetened with raisins.

Media Studies

  • noun a journalist’s source who is secretly reporting on the activities of an organisation


  • noun someone who anonymously reveals sensitive information about the organisation they work for

Origin & History of “mole”

English has four distinct words mole. The oldest is ‘brown spot’ (OE). It is the descendant of Old English māl, which meant broadly ‘discoloured mark’. This developed in middle English to ‘spot on the skin’, but the specific sense ‘brown mark’ did not emerge until fairly recently. The word goes back to a prehistoric Germanic *mailam, a derivative of a base meaning ‘spot, mark’ which also produced German malen ‘paint’ and Dutch maalen ‘paint’ (source of English maulstick ‘stick used as a rest by painters’ (17th c.)).

Mole the animal (14th c.) was borrowed from Middle Dutch mol. No one knows for sure where this came from, but its similarity to the now obsolete mouldwarp ‘mole’ (14th c.) (a compound noun whose etymological meaning is ‘earth-thrower’) suggests that it could represent a truncated version of mouldwarp’s prehistoric Germanic ancestor. The metaphorical application of the word to a ‘traitor working secretly’ has been traced back as far as the 17th century, but its modern currency is due to its use by the British espionage writer John le Carré.

Mole ‘harbour wall’ (16th c.) comes via French môle and medieval Greek mólos from Latin mōlēs ‘mass, massive structure’. The diminutive form of this, coined in modern times, is mōlēcula, from which, via French molécule, English gets molecule (18th c.). other relatives are demolish and, possibly, molest (14th c.), which comes ultimately from Latin molestus ‘troublesome’, connected by some scholars with mōlēs. And German mol, a convenient shortening of molekulargewicht ‘molecular weight’, has given English its fourth mole (20th c.), used as the basic unit of measurement for the amount of a substance.