Reverend often slipping tongue in kisser (7)
I believe the answer is:
spooner
'kisser' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see an association between them that I don't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for spooner that I've seen before include "Initial-transposing clergyman" , "One known for speech transpositions" , "He exchanged letters amusingly" , "English clergyman and Oxford don (1844-1930), who had an "ism" named after him" , "Oxford academic notable for mixing up his syllables when talking, d. 1930" .)