[countable] (informal) an illness that is usually fairly mild but spreads easily from person to person.

[countable] a fault in a machine, especially in a computer system or program See bug in the Oxford Advanced Learner's Dictionary.

​bug something to put a special device (= a bug) somewhere in order to listen secretly to other people's conversations. They bugged her hotel room.

bug somebody (informal) to annoy or irritate someone Stop bugging me! It's something that's been bugging me a lot recently. She's really beginning to bug me.

There are 19 meanings listed in OED's entry for the noun bug, one of which is considered derogatory. See 'Meaning & use' for definitions, usage, ...

1. a1425– An imaginary evil spirit or creature; a bogeyman. Also: an object or source of (esp. needless) fear or dread; an imaginary terror.

bug out (informal) (North American English, Australian English) to leave a place or situation, especially because it is becoming dangerous.

/ˈmeɪ bʌɡ/ (also cockchafer) ​a large brown insect that flies and makes a loud noise in early evening in summerTopics Insects, worms, etc. Definitions on the ...

2to leave a place or situation, especially because it is becoming dangerous We should bug out now before it's too late. They decided it was time to bug out. 3to ...

bug noun (FAULT) ... a mistake or problem in the way something works: He said they had eliminated all the bugs in the software, and we hoped this was true.