Some popular ideas, dry as dust (4)
I believe the answer is:
arid
'dry as dust' is the definition.
(thesaurus)
'some popular ideas' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ARID' can be found hidden inside 'popular ideas'.
(Other definitions for arid that I've seen before include "Excessively dry" , "Parched, waterless" , "Very dry; uninteresting" , "Rainless (region)" , "Extremely dry" .)