About 51, expert can be trusted (8)
I believe the answer is:
reliable
'be trusted' is the definition.
(I've seen this before)
'about 51 expert' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'51' becomes 'LI' (roman numeral).
'expert' becomes 'able' (I've seen this before).
're'+'li'+'able'='RELIABLE'
'can' is the link.
(Other definitions for reliable that I've seen before include "Faithful" , "Can be depended upon, trustworthy" , "Unfailing" , "Dependable, trustworthy" , "Dependable, can be trusted" .)