What a fascinating language! Edderkopp = edder + kopp = poison + head. How appropriate! Sometimes really humoristic as well.
lammekoteletter - lamb chops
lamme koteletter - lame chops (by misspelling lammekoteletter)
røykfritt - no smoking, lit. "smoke-free"
røyk fritt - smoke freely
Tyverisikret - Theft proof
Tyveri sikret - Theft guaranteed
Smørbrød - Sandwich
Smør brød - Butter bread
While you're pointing out the etymology "edderkopp", I'd like to point out that those word have had their meaning changed. "Edder" doesn't mean poison in modern Norwegian, nor does "kopp" mean head. Those words would be "gift" and "hode" today.
While "kopp" is used in some expression (like rotekopp, meaning a person who makes a mess), "en kopp" means "a cup".
spiderweb is "spindelvev" (or edderkoppnett) so I'm thinking spindel and spinne may be related as well.
Kopp is probably related to the same word, as it's Kopf in German as well, but my dictionary claims it meant "something thick, bloated". Edder seems to be related to 'eiter'(another uncommon word) meaning stinging venom from an animal, according to the dictionary as well.
Source (Norwegian Nynorsk): http://www.nob-ordbok.uio.no/perl/ordbok.cgi?OPP=edder&begge=+&ordbok=begge
"Kopper" is also the word for smallpox. (I'm not sure if this is related however).
It's interesting how words have had their meanings changed...