Is modern and very bright, but said to be a slacker! (5)

I believe the answer is:

laser

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'slacker' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

I can't explain the remainder of the clue.

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(Other definitions for laser that I've seen before include "scientific device" , "Device that generates an intense beam of light" , "Device producing an intense beam of light or radiation" , "Scientific apparatus" , "light-intensifier" .)

I've seen this clue in the Evening Standard.

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