Augmented

An antonym is a word that expresses a meaning opposite to a given word. 'Augment' means to make something greater in size, amount, or degree - to increase or enlarge it. So its antonym must convey a decrease or reduction, not an increase.

Among the given options, 'Compress' means to reduce something to a smaller size, volume, or degree by squeezing or pressing it together. Reducing size/degree is the converse of augmenting (increasing) it, which makes 'Compress' the option whose meaning is most clearly opposed to 'Augmented' among those given.

• Insignificant means unimportant or trivial. This is the opposite of 'significant', not of 'augmented' - it describes importance, not an increase or decrease in size or amount.

• Undermined means to weaken or damage the strength, authority, or confidence of something gradually. This is the opposite of 'strengthened' or 'reinforced', not of 'augmented'.

• Demolish means to completely destroy or tear down a structure. This is the opposite of 'build' or 'construct', describing destruction rather than a reduction in size or amount.

Hence, among the given options, 'Compress' is the word most opposite in meaning to 'Augmented'.