wor·ry 
(wûrē, wŭrē)
(wûrē, wŭrē)v. wor·ried, wor·ry·ing, wor·ries
v.intr.
1. To feel uneasy or concerned about something; be troubled. See Synonyms at brood.
2.
a. To seize something with the teeth and bite or tear repeatedly: a squirrel worrying at a nut.
b. To touch or handle something nervously or persistently: worry at a hangnail.
c. To attempt to deal with something in a persistent or dogged manner: worried along at the problem.
v.tr.
1. To cause to feel anxious, distressed, or troubled. See Synonyms at trouble.
2.
a. To seize with the teeth and bite or tug at repeatedly: a dog worrying a bone.
b. To touch or handle nervously or persistently: worrying the loose tooth.
c. To attack roughly and repeatedly; harass: worrying the enemy ships.
d. To bother or annoy, as with petty complaints.
e. To attempt to deal with in a persistent or repeated manner: Analysts have worried the problem for a decade.
3. To chase and nip at or attack: a dog worrying steers.
n. pl. wor·ries
Idiom: 1. The act of worrying or the condition of being worried; persistent mental uneasiness: "Having come to a decision, the lad felt a sense of relief from the worry that had haunted him for many sleepless nights" (Edgar Rice Burroughs).
2. A source of nagging concern or uneasiness.
not to worry Informal
There is nothing to worry about; there is no need to be concerned: "But not to worry: it all ... falls into place in the book's second half, where the language is plainer" (Hallowell Bowser).
[Middle English werien, worien, to strangle, from Old English wyrgan; see wer-2 in the Appendix of Indo-European roots.]
worri·er n.
Word History: The ancestor of worry, the Old English verb wyrgan, meant "to strangle." Its Middle English descendant, worien, kept this sense and developed the new sense "to grasp by the throat with the teeth and lacerate" or "to kill or injure by biting and shaking." This is the way wolves might attack sheep, for example. In the 1500s worry began to be used in the sense "to harass, as by rough treatment or attack" or "to assault verbally," and in the 1600s the word took on the sense "to bother, distress, or persecute." It was a small step from this sense to the main modern senses "to cause to feel anxious or distressed" and "to feel troubled or uneasy," first recorded in the 1800s.