Couple of questions for you --
You say that you're "starting to learn Greek" -- what does this mean exactly? Are you working through a textbook? How far have you gotten? I ask this because it makes a difference in how I answer you and what knowledge I can assume you already have and what you don't.
Second question: what dictionaries are you using?
I own the Intermediate Liddell Scott Greek-English Lexicon, this is pretty standard and what most students of classical Greek are told to purchase. It's adequate for most needs unless you're reading authors with a love of obscure vocabulary.
Looking up words can take a bit of practice, as it's not always simple to identify the headword that you should be looking under.
Looking at my dictionary, it includes an entry for βασκανος
: "slanderous, envious, malignant"πολυμεριμνος
is not in my dictionary, but under μεριμνα
I find: "care, thought, expecially anxious thought"πολυ-
is a common prefix, particularly in Homer, used for epithets. It means "many" or "full of"
There's nothing to do with "νους" here.
It is quite common to find -ν- added to a noun stem to form an adjective.
-ους is the accusative plural ending for o declension nouns and adjectives.
For future searches, there's also a useful tool at the Perseus Digital Library: Dictionary Entry Lookup
If this isn't bookmarked, it should be.