meaning of sly

[Mudko]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #544 "English Slang Idioms (147)", question 5

"We are taking care of Wes's dog on the ......... at the moment until he gets back from his business trip. We are not allowed to have a dog in this apartment complex but we agreed to watch the dog for a week since it is unlikely we will be caught in that amount of time," Rex told Pat.

(a) underground
(b) spy
(c) sly
(d) down and under

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #544 "English Slang Idioms (147)", answer 5

"We are taking care of Wes's dog on the sly at the moment until he gets back from his business trip. We are not allowed to have a dog in this apartment complex but we agreed to watch the dog for a week since it is unlikely we will be caught in that amount of time," Rex told Pat.

Correct answer: (c) sly
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what sly means?

Mudko

[Benjamin]

to do something "on the sly" means to do something in a way intended to escape notice
basically to do something you are not supposed to do and trying not to be found.

In this case the thing that is not allowed is to have a dog in the apartment complex. The person they are trying to hide the dog from is the landlord.

the word "sly" by itself means "cunning, clever"