Definition of *augment* by [Dictionary.com](http://dictionary.reference.com/browse/augment):

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> to make larger; enlarge in size, number, strength, or extent; increase
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Definition of *increase* by [Dictionary.com](http://dictionary.reference.com/browse/increase):

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> to make greater, as in number, size, strength, or quality; augment; add to
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I cannot find the difference because the definition of the 2 words are the same.

For example,
*"her secretarial work helped to **augment** her husband's income"*

Wouldn't it mean the same if I replace it with *increase*?