Fraud succeeded with one pair of unknowns (5)
I believe the answer is:
swizz
'fraud' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'succeeded with one pair of unknowns' is the wordplay.
'succeeded' becomes 's' (genealogical abbreviation).
'with one pair of' becomes 'wi' (I can't justify this - if you can you should give a lot more credence to this answer).
'unknowns' becomes 'zz' (two Z's - unknown values in algebra).
's'+'wi'+'zz'='SWIZZ'
Can you help me to learn more?
(Other definitions for swizz that I've seen before include "Rip-off" , "Racket" , "Diddle" , "Mild swindle" , "Informally a swindle or disappointment" .)