Concealed in both ideas (3)
I believe the answer is:
hid
'concealed' is the definition.
('hide' can be a synonym of 'conceal')
'in both ideas' is the wordplay.
'in' says the answer is hidden in the clue.
'HID' is hidden in the letters of 'both ideas'.
(Other definitions for hid that I've seen before include "Concealed, kept secret" , "Shrouded" , "Concealed from sight" , "Kept out of sight" , "Concealed (oneself?)" .)