infiltrate
eavesdropping
The word you are looking for is "conspire". It means to plan something secretly with others.
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Peep.
secretly talk
invade
If by secretly you meant cautiously then walking stealthily or tip toeing .
peep
Plotted, conspired.
surreptitious broken down into its word parts: sub- or its variant (in this case)sur- means "less than normal, under, below, secretly" + -rap- which means "to seize" (other words containing the same word part are rape, ravish, rapture, rapacious, raving) + -ious which means "full of, tendency to, characteristic of" so literally surreptitious means "secretly seizing characteristic".A mnemonic acronym to recall the meanings for sub- is you're secretly SUBLeTtiNg (secretly, under, below, less than normal) a sub to an unsuspecting diplomatic tenant.
There is no such word. The word secrete is a verb (to release fluid) and secret means hidden or private. The word secretly is an adverb (in a secret or covert manner).
it is an adjective that means done secretly; During my clandestine visits