1) Cautiously 2) Clandestinely 3) Covertly 4) Craftily 5) In a furtive manner 6) On the sly 7) Quietly 8) Secretly 9) Silently 10) Slyly 11) Sneakily 12) Stealthily 13) Surreptitiously 14) Underhandedly 1) Clandestinely 2) On the sly 
• (adv.) Stealthily by theft.
Fur'tive·ly adverb Stealthily by theft. Lover. 
[adv] - in a furtive manner
adverb in a furtive manner; `the soldiers were furtively crawling through the night`