Sea Lord involved in trials (7)
I believe the answer is:
ordeals
'trials' is the definition.
(I know this)
'sea lord involved' is the wordplay.
'involved' is an anagram indicator (involved can mean confusing or complex).
'sea'+'lord'='sealord'
'sealord' anagrammed gives 'ORDEALS'.
'in' is the link.
(Other definitions for ordeals that I've seen before include "Testing experiences" , "Difficult experiences, hard times" , "Tribulations" , "difficult tests" , "Trying experiences" .)