Based on the common root "arch," the meaning that these words have in common is:
- They all refer to the primary person in a situation.
Here’s how they relate:
- Monarch: A monarch is a primary ruler or leader (king or queen).
- Arch-enemy: An arch-enemy is a principal enemy or primary opponent.
- Architect: An architect is the primary designer or chief builder.
Thus, the correct answer is that they all refer to the primary person in a situation.