/ məʊl; NAmE moʊl/ noun
1.
a small animal with dark grey fur, that is almost blind and digs tunnels under the ground to live in
—see also molehill
2.
a small dark brown mark on the skin, sometimes slightly higher than the skin around it
—compare freckle
3.
a person who works within an organization and secretly passes important information to another organization or country
4.
( chemistry ) a unit for measuring the amount of substance
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WORD ORIGIN
sense 1 and sense 3 late Middle English : from the Germanic base of Middle Dutch and Middle Low German mol .
sense 2 Old English māl discoloured spot , of Germanic origin.
sense 4 early 20th cent.: from German Mol , from Molekul , from Latin molecula , diminutive of Latin moles mass.