ἀσύνετος is α- (not) plus συνετός, intelligent or understanding. Strong’s defines it as unintelligent. Thayer gives unintelligent, without understanding for Mark 7:18 and Matthew 15:16, and notes a harsher “stupid” sense in Romans.

συνετός comes from συνίημι, to put together, to comprehend. The word is not mere dullness of mind. It names a failure to synthesize: facts are there, and they are not put together into discernment. That is why this Bible prints “undiscerning” in Mark and Matthew, not “dull” or “foolish.” Foolishness in this paragraph of Mark is a different word, ἀφροσύνη, later in Mark 7:22.

In Mark the link is deliberate. In Mark 7:14 Yahshua tells the crowd σύνετε, understand. In 7:18 he asks if the disciples are ἀσύνετοι. They were told to put it together, and they have not. Οὕτως adds force: “Are you also so undiscerning?” Matthew’s parallel uses ἀκμήν, still, instead of οὕτως.

The lexical force is lack of understanding. The scenes often show more than an empty head. In Mark the rebuke follows a command to understand and a second question, οὐ νοεῖτε, don’t you perceive? In Romans the same adjective sits with people who knew God and would not honor him (Romans 1:21, 1:31). That context supports reading unwilling, lazy discernment—willing ignorance—without turning the dictionary gloss into “foolish” or “dull.”

This Bible prints “undiscerning” wherever the Greek is ἀσύνετος.