Crossword Genius

Long boring speech illustrating singular belief … (6)

Ross

I believe the answer is:

screed

'long boring speech' is the definition.
(a screed is a tedious speech or piece of writing)

'singular belief' is the wordplay.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'belief' becomes 'creed' (creed is a kind of belief).
's'+'creed'='SCREED'

'illustrating' is the link.

(Other definitions for screed that I've seen before include "Tiresomely long letter about creeds" , "Long tedious piece of writing" , "Lengthy piece of writing" , "Layer applied to floor" , "Lengthy statement" .)

I've seen this clue in The Guardian.
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