1 tell-tale

2 informer (esp. to police)

3 whistleblower

4 grass

1 secret code

2 ciphertext

3 password

4 PIN

1 classroom

2 classifier: 间 jiān

1 secret

2 classifier: 个 gè

1 intimate

2 close

1 to be discontented with one's home

2 to have adulterous relations after marriage (of women) (idiom)

1 lit. to reach the main room and enter the chamber (idiom)

2 fig. to gradually attain proficiency

3 to attain a higher level

1 wielding the halberd within the household (idiom); internecine strife

1 inextricably linked (idiom)

2 inseparable

1 to show the wolf into the house (idiom)

2 to introduce a potential source of trouble