The size is the message. A large spider is read as a web-weaving presence grown too big to ignore — in the East an entangling matter at the center of its web, in the West the devouring side of care and control, in Ibn Sirin's tradition a weak but insidious adversary made large.
Three readings
In Chinese tradition · 周公解梦
The Chinese reading watches the web more than the spider: a great spider marks a matter that has been weaving quietly and now sits at the center of many threads — obligations, schemes, entanglements. Fortune-readings exist too — a spider descending was sometimes read as luck arriving on its thread — but a looming spider asks whose web you are in, and how long it has been spinning.
In the Jungian reading the spider tends toward the negative pole of the mother-image and of control: the weaver whose care becomes a web, the relationship or pattern that feeds on what it holds. A big spider is that pattern grown dominant. Fear of it usually marks entanglement you feel but have not named — a job, a bond, a habit at whose center something patient waits.
Ibn Sirin read the spider as a weak enemy — its house, as the Qur'an has it, the frailest of houses. A big spider magnifies the paradox: an adversary or entanglement that looks formidable but whose real strength is only the web you have not yet brushed away. As meaning: name the entanglement, and note that the tradition insists it is weaker than it appears.
It marks entanglement rather than doom — a web-weaving matter grown large. Notably, the Islamic tradition insists the spider's house is the frailest of houses: what looms is weaker than it looks.
What does killing the spider mean?
Across traditions, overcoming it reads as breaking the entanglement — ending an insidious pattern or prevailing over a scheming rival. It is generally the most favorable outcome of the dream.
What about many spiders?
Multiplication reads as many small entanglements rather than one great one — a life webbed over with minor obligations, anxieties, or schemers. The dream asks which threads to cut first.
This is the general reading. Your dream is specific.