bug 
(bŭg)
(bŭg)n.
1.
a. An insect having mouthparts used for piercing and sucking, such as an aphid, a bedbug, or a stinkbug.
b. An insect of any kind, such as a cockroach or a ladybug.
c. A small invertebrate with many legs, such as a spider or a centipede.
2.
a. A disease-producing microorganism or agent: a flu bug.
b. The illness or disease so produced: took several days to get over the bug.
3.
a. A defect or difficulty, as in a system or design.
b. Computers A defect in the code or routine of a program.
4. An enthusiasm or obsession: got bitten by the writing bug.
5. An enthusiast or devotee; a buff: a model train bug.
6. An electronic listening device, such as a hidden microphone or wiretap, used in surveillance: planted a bug in the suspect's room.
v. bugged, bug·ging, bugs
v.intr.
To grow large; bulge: My eyes bugged when I saw the mess.
v.tr.
Phrasal Verbs: 1.
a. To annoy; pester.
b. To prey on; worry: a memory that bugged me for years.
2. To equip (a room or telephone circuit, for example) with a concealed electronic listening device.
3. To make (the eyes) bulge or grow large.
bug off Slang
To leave someone alone; go away.
bug out Slang
Idiom: 1. To leave or quit, usually in a hurry.
2. To avoid a responsibility or duty. Often used with on or of: bugged out on his partners at the first sign of trouble.
put a bug in (someone's) ear Informal
To impart useful information to (another) in a subtle, discreet way.
[Perhaps alteration (influenced by obsolete bug, hobgoblin; see BUGBEAR) of Middle English boude, budde, beetle, weevil, from Old English -budda as in scearnbudda, dung beetle; akin to Low German dialectal budde, louse.]
bugger n.