Ignoring the odds, Keynes queried guarantee (6)
I believe the answer is:
ensure
'guarantee' is the definition.
(I know that guarantee can be written as ensure)
'ignoring the odds keynes queried' is the wordplay.
'ignoring the odds' means one should take alternating letters (letters in odd-numbered positions are removed).
'keynes'+'queried'='keynesqueried'
The alternate letters of 'keynesqueried' are 'ENSURE'.
(Other definitions for ensure that I've seen before include "Make certain, clinch" , "Make certain, confirm" , "Guarantee" , "Protect" , "Make certain or safe" .)