In a code language, 'mok dan sil' means 'nice big house';
'fit kon dan' means 'house is good' and
'warn tir fit' means 'cost is high'.
Which word stands for 'good' in that language ?
In the first and second statements, the common code word is 'dan' and the common word is 'house'.
So, 'dan' means 'house'.
In the second and third statements, the common code word is 'fit'.
So 'fit' stands for 'is'.
Thus, in the seccond statement, 'kon' stands for 'good'.