The most common and most likely answer to this crossword clue is the 7 letter word WINKING
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More clues leading to the result WINKING
Buddy explains!

The straight part
We know that "conniving" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case conniving = winking.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WINKING mean?
WINKING verb- To close one's eyes in sleep.
- To close one's eyes.
- Usually followed by at: to look the other way, to turn a blind eye.
- To close one's eyes quickly and involuntarily; to blink.
- To blink with only one eye as a message, signal, or suggestion, usually with an implication of conspiracy. (When transitive, the object may be the eye being winked, or the message being conveyed.)
- To gleam fitfully or intermitently; to twinkle; to flicker.
- The act of someone who winks.