Monotony of chaps in rough seas bearing south (8)
I believe the answer is:
sameness
'monotony' is the definition.
(synonyms)
'chaps in rough seas bearing south' is the wordplay.
'chaps' becomes 'men' (I've seen this before).
'in rough' indicates an anagram (I've seen this in other clues).
'bearing' is an insertion indicator.
'south' becomes 's' (synonyms).
'seas' anagrammed gives 'saes'.
'men' going within 'saes' is 'samenes'.
'samenes'+'s'='SAMENESS'
'of' acts as a link.
(Other definitions for sameness that I've seen before include "Tedious monotony" , "Lack of variety" , "Unchanging quality" .)