grand- Also great-.
The second degree of parentage or descent.
[From Latin grandis, great]
English borrowed this prefix from French, in which it refers only to parentage, as in English grandfather and grandmother for the parents of one's parent (in general grandparent). In French the corresponding term for degrees of descent is petit, little, but English adopted grand- for both situations, as in grandson or granddaughter for the child of one's child, or more generally grandchild.
Further degrees of separation by generations are indicated by prefixing great-: great-grandfather, great-granddaughter. Both can sometimes be used for relationships at one remove: great-aunt (also grand-aunt), the aunt of one's father or mother; great-nephew (also grand-nephew), the son of one's nephew or niece.