der Großvater
grandfather
The father of one's own father or mother.
Mein Großvater erzählt mir oft Geschichten aus seiner Jugend.
My grandfather often tells me stories from his youth.

grandfather
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grandfather
The father of one's own father or mother.
Mein Großvater erzählt mir oft Geschichten aus seiner Jugend.
My grandfather often tells me stories from his youth.

The word is simply made up of 'groß' (big/great) and 'Vater' (father). 'Groß-' is used here in the sense of 'one generation before,' not in the sense of physical size.
Mein Großvater ist kleiner als mein Vater.
My grandfather is shorter than my father.
In everyday life, and especially when talking with family, the short form 'Opa' (grandpa) is almost always used. 'Großvater' (grandfather) is more formal and is used more in written language.
Am Sonntag besuchen wir Opa und Oma.
On Sunday we are visiting Grandpa and Grandma.
The prefix 'Groß-' refers to your parents' parents' generation. It also works for other family members, for example 'die Großmutter' (grandmother/grandma) and 'die Großeltern' (grandparents; grandma and grandpa together).
Meine Großeltern leben auf dem Land.
My grandparents live in the countryside.
father
'der Vater' and 'der Großvater' both belong to the family and refer to male relatives. 'der Vater' is the male parent of a child. 'der Großvater' is one generation older: he is the father of the mother or father. The words can be confused because both often appear in a family context and are connected with children. A practical tip: the father has a child; the grandfather has a grandchild.

Beim Frühstück erzählt Frau Hofmann von ihrem Großvater.
At breakfast, Ms. Hofmann talks about her grandfather.
Leas Vater hilft ihr heute bei den Hausaufgaben.
Lea's father is helping her with her homework today.