grandfriend means A friend of the same generation or age as a grandparent. Lexicurio rates it Sui generis — a strength score of 88 out of 100.
Etymology
From grand- + friend.
noun
- A friend of the same generation or age as a grandparent.“One high school has “Senior Teas” on a fairly regular basis, bringing senior citizens and teenagers together in a social setting. Other communities have students adopt a senior citizen as a “grandfriend” and have regular get-togethers”