Lecture given by moaners, who've somehow lost an article (6)
I believe the answer is:
sermon
'lecture' is the definition.
(sermon is a kind of lecture)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for sermon that I've seen before include "minister's speech" , "Address of a religious nature" , "Preachment" , "Homily" , "Speech in church" .)