Furtive means "attempting to avoid notice or attention, typically because of guilt or a belief that discovery would lead to trouble." Secretive means "inclined to keep things secret."

The other options are not as appropriate synonyms for furtive.

• Abortive means "failing to produce the intended result."
• Adhesive means "able to stick fast to a surface or object."
• Positive means "constructive, optimistic, or confident."