O lord, what a mess - simply drivel! (5)
I believe the answer is:
drool
'simply drivel' is the definition.
'drool' can be an answer for 'drivel' (synonyms). I'm not certain of the 'simply' bit.
'o lord what a mess' is the wordplay.
'what a mess' indicates anagramming the letters.
'o'+'lord'='olord'
'olord' anagrammed gives 'DROOL'.
Can you help me to learn more?
(Other definitions for drool that I've seen before include "Slobber" , "Show excitement" , "Let saliva run from the mouth" , "dribble" , "Spill saliva" .)