Swimmer lapping one end of the complex (8)
I believe the answer is:
fiendish
'complex' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'swimmer lapping one end' is the wordplay.
'swimmer' becomes 'fish' (fish swim).
'lapping' means one lot of letters goes inside another (lapping can mean covering or wrapping).
'one' becomes 'i' (Roman numeral).
'i'+'end'='iend'
'fish' enclosing 'iend' is 'FIENDISH'.
'of the' acts as a link.
Can you help me to learn more?
(Other definitions for fiendish that I've seen before include "Very difficult" , "Terrible" , "Like Satan or the devil" , "This Sudoku" , "how diabolically cruel" .)