“That super herbicide has decimated the weeds in our garden.”
VERY strictly speaking, a herbicide kills grass (Latin herba), but I will accept that it is generally used for any weed killer. I balk, however, at decimate. The Romans had a typically brutal method of quelling rebellion in the ranks: the officers killed every tenth man in a mutinous legion to discourage the rest. Thus, decimate means to eliminate 10% of a group of people. Apart from the argument that this word should be applied only to humans, I would hope that an effective weed killer would not leave 90% of weeds still flourishing.
My reaction to “rather unique” or “very unique” is similar. There is a set of adjectives—including unique, complete, equal, and perfect —whose core meaning embraces a mathematically absolute concept and which therefore, according to a traditional argument, cannot be modified by adverbs such as really, quite, or very. For example, since the core meaning of unique (from Latin ‘one’) is ‘being only one of its kind,’ it is logically impossible, the argument goes, to sub-modify it: it either is ‘unique’ or it is not, and there are no stages in between. Rather like being – or not being – pregnant.
In practice – and this is where I realise what a pedantic stick-in-the-mud I am – the situation in the language is more complex than this. Words like unique have a core sense but they often also have a secondary, less precise (non-absolute) sense of ‘very remarkable or unusual,’ as in: a really unique opportunity. It is advisable, however, to use unique sparingly and not to modify it with: very, quite, really, etc. Often, you can instead make accurate use of: rare, distinctive, unusual, remarkable, or other non-absolute adjectives.
Words inevitably change meaning over the course of time, but it still disturbs me to hear a man (British, of course) admit to being “slightly gutted” that his football team had lost. How can one be “slightly gutted”? If you are gutted, you have been disembowelled; your guts, intestines, entrails have been removed. Another mathematically absolute concept, I would say. Is this good old British understatement? Or perhaps he had had a minor colectomy?