was bound to take

Question

Context:

The day after the shooting of Don Corleone was a busy time, for the Family. Michael satyed by the phone relaying messages to Sonny. Tom Hagen was busy trying to find mediator satisfactory to both parties so that a conference could be arranged with Sollozzo. The Turk had suddenly become cagey, perhaps he knew that the Family button men of Clemenza and TEssio were ranging far and wide over the city in attempt to pick up his trail. But Sollozzo was sticking close to his hideout, as were all top members of Tattaglia Family. This was expected by Sonny, an elementary precaution he knew the enemy was bound to take.

Couldn't you explain of the phrase in the context?

Answer 1

Bound to do something uses the definition of bound found here.

bound(adj.) certain to do or have something

It is from the idea of binding or tying something; the person an action are linked together tightly.

In this case, Solozzo is staying close to his hideout while he is being tracked. Sonny knows that Solozzo is certain to take that precaution.

Answer 2

This was expected by Sonny, an elementary precaution he knew the enemy was bound to take.

By the definition of bound usage #2, sense 4;:

4) certain; sure; destined ⇒ "bound to lose"

So the meaning is like:

This was expected by Sonny, an elementary precaution he knew the enemy was certain/sure/destined to take.