October was the month of the ancient Bacchanals, the rites in honour of Dionysus, were people tried to burst free from formality into a world of divine freedom and chaos.
They provoked this state by means of large amounts of wine, but likely also with a cocktail of fermented sap from the silver-fir, laced with amanita muscaria and ivy. Possibly they also chewed ivy-leaves. Resulting in frenzies during which animals, children and even adult men (most revellers were women) were torn to pieces…
Fortunately (for the women) ivy can also cure headaches: its leaves formed the wreath of Bacchus, and thus he prevented hangovers.
Ivy-leaves were also used to crown the heads of poets.
For the druids, ivy was one of the most powerful plants, because it can strangle to death even the mightiest oak. It was a portent of death, a symbol of strength and - because it grows spirally - of spiritual growth.

A deity associated with ivy is the Gallic goddess Epona. Among Epona's attributes are a cornucopia, which suggests she was originally a fertility goddess, but mostly she's associated with horses; she even was adopted by the Roman soldiers and was the only Gallic deity with a temple in Rome.
The cult of Epona was brought by the Romans to the British isles, but there of course she was already venerated as Rhiannon (Wales) or Macha (Ireland). Epona/Rhiannon/Macha is quite heroic and prepared to sacrifice herself, a feature of horse-worship demonstrated again by Vercingetorix, who at his last stand against the Romans, sent his horses behind the lines to avoid their slaughter, and faced his enemies on foot.

The boar was an important animal in Celtic art and warfare: this ferocious and cunning animal was said to lead the Celtic warriors in battle and its effigy decorated battle-trumpet, helmet and shield. The boar can thus be seen as a war god in animal form.
A boar named Twrch Trwyth was one of King Arthurs most terrible foes.
Probably because it could only be defeated by someone able to pronounce its name correctly.

The Ogham sign attributed to this month is Gort.