Getting cross is really foolish (3)
I believe the answer is:
mad
This could be a double definition.
'getting cross' is the first definition.
'mad' can be an answer for 'cross' (thesaurus). I'm unsure of the 'getting' bit.
'really foolish' is the second definition.
'mad' can be an answer for 'foolish' ('mad' can be similar in meaning to 'foolish'). I'm not certain of the 'really' bit.
'is' is the link.
Can you help me to learn more?
(Other definitions for mad that I've seen before include "Demented or excited or angry" , "Frantic" , "lunatic" , "Deranged" , "abandoned" .)