stealth

The cat stealthily crouched in the grass eyeing its intended victum and waiting for just the right moment to pounce.

(stealthy,stealthily)

sneaky

malevolent

The malevolent spirit howled profanities through the night from the depths of the old basement

(malevolently)

wicked or evil 

assuage

It took 3 years for my feelings of grief to assuage after the death of my father.

(assuaged,assuages, assuaging)

to make something uncomfortable feel better.

dictum

There is an old dictum which states "Might makes right", but i disagree.

(dictation)

a short statement that expresses a general truth or principle

arbitrate

If your two best friends are fighting over the last piece of gum in the pack, you might arbitrate by telling them to split it.

(-d,-ing,-s)

to act between parties to resolve their differences.

nauseate

The first few weeks of her pregnancy were difficult because Katy woke up every morning feeling nauseated and dizzy

(-d,-ing,-s,nausea, nauseous)

to feel sick to the point of almost vomiting

melancholy

The one act play was so melancholy that i felt depressed even after i left the theater!

(melancholic)

gloomy or depressed

aloof

After the third time, Michael realized she wasn't shy, just aloof, because she hardly spoke and acted bored every time they went out.

(aloofly)

not friendly or forthcoming; cool and distant

benign

Until Jen and Dill excluded me from their plans, she was only another lady in the neiborhood, but a relatively benign presence.

(benignly)

showing or expressing kindness or gentleness

acquiesce

We were accustomed to prompt, if not always cheerfully acuiescing to Atticus's instructions, but from the way he stood Jen was not thinking of budging.

(acquiesced,aquiesces,aquiescing)

submit or comply silently or without protest; agrees consent