Significant eccentricity observed in bloke in Gulf working (10)
I believe the answer is:
meaningful
'significant' is the definition.
(associated in meaning)
'eccentricity observed in bloke in gulf working' is the wordplay.
'eccentricity' becomes 'E' (geometry abbreviation).
'observed in' indicates putting letters inside.
'bloke' becomes 'man' (informal term for a man).
'working' indicates an anagram.
'e' placed within 'man' is 'mean'.
'gulf' with letters rearranged gives 'gful'.
'mean'+'in'+'gful'='MEANINGFUL'
(Other definitions for meaningful that I've seen before include "Important" , "Significant" .)