IPA: /ˈʌpərpɑːrt/
KK: /ˈʌpərˌpɑrt/
A section located at the top or higher position of something, often referring to parts of a bird's body such as the back or wings.
The ornithologist noted the distinct colors of the upperpart of the bird during the observation.
Upperpart → It is formed from "upper" (from Old English "uper", meaning higher or above) and "part" (from Latin "partem", meaning a piece or portion). The word "upperpart" refers to the higher portion of something.
Think of 'upper' meaning higher and 'part' meaning a piece — so 'upperpart' refers to the higher piece of something.
No commonly confused words.