IPA: /ˈɡrændˌʌŋkəl/
KK: /grændˈʌŋkəl/
A relative who is the brother of one of your grandparents.
My granduncle shared many stories about our family history.
Granduncle is formed from "grand" (from Old French *grand*, meaning large or great) and "uncle" (from Latin *avunculus*, meaning maternal uncle). The term refers to the brother of one's grandparent, thus indicating a familial relationship that is 'great' or 'large' in the generational sense.
Think of 'grand' meaning large or great, and 'uncle' referring to a family member. This helps you remember that a granduncle is a great uncle, or the brother of your grandparent.
No commonly confused words.