I think we may be dealing with two similar words here...

For the record, the word used in The Hobbit is "Attercop". Move a couple of vowels around, drop the "o", and you have "Ettercap" -- which is totally not legally actionable, except that if you change a couple of letters around and use it yourself, TSR/WotC/Hasbro will totally sue your pants off.

Attorcroppe (alternate spelling "attercroppe") means "little venom head" and is described in multiple sources as a fairy that looks like a small snake with human arms and legs and walks upright.

If these are the same word, I don't know how to reconcile Tolkien's spiders with the snake-fairies.