Anonymous male swimming in Scottish loch (8)
I believe the answer is:
nameless
'anonymous' is the definition.
(similar in meaning)
'male swimming in scottish loch' is the wordplay.
'swimming' indicates an anagram (letters swim around into a new order).
'in' indicates putting letters inside.
'scottish loch' becomes 'ness' (I've seen this before).
'male' anagrammed gives 'amel'.
'amel' inserted inside 'ness' is 'NAMELESS'.
(Other definitions for nameless that I've seen before include "This undistinguished" , "Untitled" , "not easily identified?" , "Unidentified" , "Salesmen lacking identity" .)