worry-n; 2 Senses

Sense Number 1: a cause or source of anxiety, concern

Commentary: WORRY[+cause][+effective][+anxiety]
NOTE: refers to an external cause of concern, not an internal emotion
NOTE: of the form X BE worry

Her son has been a constant source of worry for her.
One of their biggest worries at the event will be crowd control.
Inflation remains a worry for the economy. ('remain' implies 'be')
Terrorists are a continuing worry to the airline industry. (Note difference in structure here from related sentence in Sense 2)

WordNet 3.0 Sense Numbers: 1

Sense Number 2: an emotional state of anxiety

Commentary: WORRY[+state][+emotional][+anxiety]
NOTE: refers to an internal emotional state of anxiety
NOTE: of the form X's worry, or 'there is worry THAT S' (a proposition)

John's worries about money kept him awake at night.
I could see the worry in her face.
There is some worry that terrorists could jam satellite communications. (implies a proposition, which is a belief/concern held by someone)
Bob's worry is that he may get laid off next month.

WordNet 3.0 Sense Numbers: 2