Phonetic variant of William, from Germanic wil (will, desire) and helm (protection), meaning 'resolute protector'.
Willum is a phonetic variant of William, from Germanic elements meaning will or desire and helm or protection, together suggesting a resolute protector. That classic meaning has made William one of the most enduring names in the English-speaking world.
Willum preserves the core but gives it a more colloquial, slightly old-country feel. In use, Willum feels sturdy, familiar, and faintly rustic. It has the warmth of a spoken nickname while remaining recognizably tied to a major traditional name.
The altered vowel shape makes it feel less formal and more intimate. Willum is a good example of how a classic can be softened without losing its underlying strength.