Nab rejected béarnaise sneakily because it's more convenient (6)
I believe the answer is:
easier
'it's more convenient' is the definition.
(I've seen this in another clue)
'nab rejected bearnaise sneakily' is the wordplay.
'rejected' indicates named letters should be taken away.
'sneakily' indicates an anagram (a tricksy or sneaky ordering of the letters).
'bearnaise' with 'nab' removed is 'eraise'.
'eraise' is an anagram of 'EASIER'.
'because' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for easier that I've seen before include "Less taxing" , "Posing less difficulty" , "Requiring less effort" , "More simple" , "Not so hard" .)