That speaks volumes!
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The idiom refers to the information contained in a series of book volumes.
The expression became common as early as the first half of the 19th century. The first written record of it dates from 1842.
The proverb means "something says it all" or "something is very revealing".
Two examples:
a) After another defeat, there were no vehement assurances from the club management this time that the coach had full confidence, which speaks volumes.
The club management no longer openly spoke out in his favour, so the coach is no longer firmly in the saddle after various defeats.
a) When I asked Aunt Helen how she liked my new dress, she grimaced wordlessly. That spoke volumes!
There is no need for a verbal statement in this case, it is already clear from her facial expression that the dress is not well received by Aunt Helen.
