Sathyaish, I would go to the dictionary for the basic definitions:
IDIOM – an expression whose meaning is not predictable from the usual meanings of its constituent elements, as ‘kick the bucket’ – to die.
PROVERB – a short popular saying, usually of unknown and ancient origin, that expresses effectively some commonplace truth or useful thought, as ‘a stitch in time saves nine’ – prompt attention to minor problems will avoid bigger problems later (or literally, take care of one loose stitch now and you may avoid having to sew up nine stitches later)
METAPHOR – a figure of speech in which a word or phrase that ordinarily designates one thing is used to designate another, thus making an implicit comparison, as in “a sea of troubles” or “All the world's a stage” (Shakespeare)
So what are the differences and relationships between the three? Well, there are no hard and fast rules but, for example, proverbs are usually old. How, old a saying must be to be a proverb is not definite, but there aren’t a lot of 10-year-old proverbs floating around.
Can a proverb also be an idiom or an idiom be a proverb? It is conceivable, that a proverb could also be an idiom, but it would probably be called a proverb rather than as idiom – I suppose the age taking precedence. One could ask if the proverb ‘a stitch in time saves nine’ is also an idiom and looking at the definition one would have to ask what is meant by ‘predictable’ – what is predictable to one person may not be predictable to another, and this looks to me to be ‘a can of worms’ [idiom and metaphor, but not proverb meaning a source of many unpredictable or unexpected problems].
Can a proverb also be a metaphor or a metaphor a proverb? Well, according to the above definition a proverb could certainly contain a metaphor and if you loosely take a phrase to be a whole sentence (which many do), you might say that the whole proverb could be a metaphor. If a proverb were a metaphor, however, in a listing it would again, as with idiom, probably be listed as a proverb.
Can an idiom also be a metaphor and a metaphor an idiom? Well, idioms can and often do contain metaphors. In the idiom ‘kick the bucket’ one could say that ‘bucket’ is a metaphor for ‘life’ and ‘kick’ is a metaphor for ‘bring to an end,’ and that the whole idiom is a metaphor. And, again, if one extended ‘metaphor’ to include whole sentences, then one might say that a metaphor could also be an idiom.
As you can see this is a sticky business and it is not always entirely clear which category/categories is/are the appropriate one/ones. And, along these lines, you could also ask about cliché, which is a trite or overused expression or idea (e.g. ‘the gospel truth, ‘go the extra mile,’ ‘seeing is believing’).This is also is somewhat nebulous category since what is ‘trite’ and ‘over used’ is often a judgment call. And without going through the complete gamut of possibilities I will note that ‘seeing is believing’ is a proverb and an idiom as well as a cliché.
(Random House Webster’s Unabridged Dictionary, Merriam-Webster’s Unabridged Dictionary, American Heritage Dictionary)
Ken G – August 17, 2004
Reply from Ken Greenwald (Fort Collins, CO - U.S.A.)