Bug

An insect or similar organism, such as a centipede or an earwig. I don't like bugs crawling on me.
2. A disease-producing microorganism. The flu bug has caused many to die.
3. Computer. A defect in the code or routine of a program. A bug caused the program to give an incorrect number.
4. An electronic listening device, such as a hidden microphone or wiretap, used in surveillance. They planted a bug in the suspect's office.
5. To annoy; pester. That memory has bugged me for years.
6. To grow large; bulge. My eyes bugged when I saw the mess.