Blab about one criminal at sea (6)
I believe the answer is:
pirate
'criminal at sea' is the definition.
'pirate' can be an answer for 'sea' (thesaurus). I am unsure of the 'criminal at' bit.
'blab about one' is the wordplay.
'blab' becomes 'prate' (I've seen this in another clue).
'about' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'prate' placed around 'i' is 'PIRATE'.
Can you help me to learn more?
(Other definitions for pirate that I've seen before include "Hook", for example" , "Hook for one" , "He sailed under the Jolly Roger" , "Rover" , "Maritime robber" .)