The drab dimension (7)

I believe the answer is:

breadth

I'm a little stuck... Click here to teach me more about this clue!

'dimension' is the definition.
(I know that breadth is a type of dimension)

'the drab' is the wordplay.
'the drab' anagrams to 'BREADTH'.
Though, I'm not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for breadth that I've seen before include "Wideness" , "Liberal view" , "Lateral extent" , "Width, thickness" , "Red bath (anag)" .)

I've seen this clue in The Irish News.

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