Thick dick grabbed by boss (6)
I believe the answer is:
stupid
'thick' is the definition.
(similar in meaning)
'dick grabbed by boss' is the wordplay.
'dick' becomes 'pi' (I can't justify this - if you can you should give a lot more credence to this answer).
'grabbed by' means one lot of letters goes inside another (inserted letters are grabbed inside).
'boss' becomes 'stud' (both can mean a metal decoration).
'pi' placed inside 'stud' is 'STUPID'.
Can you help me to learn more?
(Other definitions for stupid that I've seen before include "potty" , "Not intelligent, foolish" , "Not very bright" , "Idiotic" , "Senseless" .)