Terrible bores on the wagon (5)

I believe the answer is:

sober

'on the wagon' is the definition.
(I've seen this in another clue)

'terrible bores' is the wordplay.
'terrible' indicates an anagram.
'bores' is an anagram of 'SOBER'.

(Other definitions for sober that I've seen before include "Like a judge?" , "Serious or solemn and not drunk" , "Dry - dull" , "Dignified and sombre in manner or character" , "Sedate and rational" .)

I've seen this clue in the Sydney Morning Herald.

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