Select the most appropriate one-word substitution for the given group of words. 

Careful, cautious watch on surroundings 

Circumspect

The most appropriate one-word substitution for the given group of words "Careful, cautious watch on surroundings" is "Circumspect."

Here are the explanations of the four options:

1. Interlude: "Interlude" refers to an intervening period or break between two events or activities. It does not pertain to the careful or cautious watch on surroundings.

2. Watchman: A "watchman" is a person employed to guard or keep a lookout over a particular area or property. While a watchman may be vigilant, the term does not specifically convey the careful or cautious nature of the watch.

3. Circumlocution: "Circumlocution" refers to the use of excessive words or indirect language to express an idea. It does not relate to the careful or cautious watch on surroundings.

4. Circumspect: "Circumspect" is the correct term to describe the careful, cautious, or vigilant watch on surroundings. It implies being attentive, observant, and thoughtful in assessing one's environment to avoid potential risks or dangers.