Wedding invitee loudly indulged in speculation (7)
I believe the answer is:
guessed
'wedding invitee loudly indulged' is the definition.
I can't judge whether this definition defines the answer.
'speculation' is the wordplay.
I cannot quite see how this works, but
'speculation' could be 'guess' (synonyms) and 'guess' is located in the answer.
The remaining letters 'ed' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for guessed that I've seen before include "Estimated correctly" , "Hazarded, estimated" , "perhaps got in one" , "Estimated, reckoned" , "Made estimate or hazarded opinion" .)
