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Core Words Familarize yourself with the 'core words'.
Compounds Expand your vocabulary by studying more complex words built by the 'core words'.
Etymology Explore the origin of the 'core words'.

{n}	grumble	(a low thundering, rumbling or growling sound)	Gegrummel {n}, Grummeln {n}
{n}	grumble	(the sound made by a hungry stomach)	Knurren {n}
{v}	grumble	brummen
{v}	grumble	(to murmur or mutter with discontent)	murren