IPA: /ˈɡrændˌniːs/
KK: /grændˈnis/
A grandniece is the daughter of your niece or nephew.
My grandniece is starting school this year.
Grandniece → It is formed from "grand-" (meaning great or large, derived from Old French *grant*) and "niece" (from Old French *niece*, meaning daughter of one's brother or sister). The word "grandniece" refers to the daughter of one's niece or nephew, thus indicating a generational extension of family.
Think of 'grand' as indicating a larger family connection and 'niece' as the daughter of your sibling's child — a grandniece is the daughter of your niece or nephew.
No commonly confused words.