Furtive describes something that is done in a quiet and secret way to avoid being noticed. It can also mean "expressive of stealth" or "sly" (as in "a furtive look"), or "obtained underhandedly" (as in "furtive gains").

// We exchanged furtive smiles across the table, carefully not to attract the teacher's attention.

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"Like cardinals, Carolina wrens have slowly and gradually immigrated into New Brunswick and other areas of the Maritimes…. So if we look at this little bird, what do we see? First, it 'looks' like a wren, meaning it's small with a cocked-up tail and a fairly long beak. It would also have a rather perky behaviour and furtive movements. Its coloration is quite striking, being a rich earthy brown above and deep caramel below, and another distinctive feature is a prominent white line over each eye." — Jim Wilson, The Daily Gleaner (New Brunswick, Canada), 27 Mar. 2025

You can’t steal someone’s heart without capturing their attention, nor can you steal someone’s thunder without hijacking their audience’s attention. But attention is something most thieves would rather avoid; whether stealing a glance or a diamond, one must be furtive or risk getting caught in the act. When first used in written English in the early 1600s, furtive meant "done by stealth." It later adopted the less common meaning "stolen" or "obtained underhandedly." Whichever meaning you choose, the word has a fittingly elusive ancestry, either stepping into English via the French furtif or coming directly from that word's ancestor, the Latin furtivus, itself a descendent of fur, meaning "thief."