'Dull' in the Bible

because they had not understood [the miracle of] the loaves [how it revealed the power and deity of Jesus]; but [in fact] their heart was hardened [being oblivious and indifferent to His amazing works].

And He said to them, “Are you, too, so foolish and lacking in understanding? Do you not understand that whatever goes into the man from outside cannot defile and dishonor him,

He perceived what they were saying, and He said to them, "What is this discussion of yours about having no bread? Do you not yet see and understand? Are your minds so dull of comprehension?