Lower (6)
'lower' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sadder that I've seen before include "Less happy" , "Unhappier" , "More unhappy (but hopefully 1 down)" , "More downcast" , "Lower" .)
'lower' is the definition.
(as in nether regions)
This is all the clue.
(Other definitions for nether that I've seen before include "Situated below" , "Subordinate" , "Located below" , "Underground" , "These regions are hell, the underworld" .)
'lower' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for decrease that I've seen before include "Become smaller or fewer" , "Diminish, lessen" , "Iron out the wrinkles" , "drop" , "Decline" .)
'lower' is the definition.
(depressing is a kind of lowering)
This is all the clue.
(Other definitions for depress that I've seen before include "Cause to feel dispirited" , "Make miserable or lower" , "Make dejected" , "Put dent in or make dismal" , "Make sad or gloomy" .)
'lower' is the definition.
(synonyms)
This is all the clue.
(Other definitions for let down that I've seen before include "Fail to meet expectations of others" , "Disappointment < lowered" , "deflating" , "Failed - deflated" , "Failed - to deflate a tyre - disappointed" .)