Crossword Genius

They may be light, but you can't really raise them (4)

Ross

I believe the answer is:

rays

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'they' is the definition.
Both the answer and definition are plural nouns.
Maybe they are linked in a way I don't understand?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for rays that I've seen before include "Fish with wing-shaped fins and long tails" , "Columns of light or heat" , "Sunbeams" , "Flat fish" , "shafts" .)

I've seen this clue in the Evening Standard.
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