IPA: /ˈʌndərˌkærɪdʒ/
KK: /ˈʌndərˌkærɪdʒ/
The part of a vehicle or aircraft that supports it from below, including the wheels and other structures that help it move or land safely.
The mechanic inspected the undercarriage of the car for any signs of damage.
Undercarriage is formed from "under" (meaning beneath) and "carriage" (from Old French *carriage*, meaning a vehicle or the act of carrying). The word refers to the part of a vehicle that is beneath it, supporting it and allowing it to move.
Think of something that is 'beneath' ('under') a vehicle that helps it 'carry' ('carriage') itself — that's what undercarriage means.
No commonly confused words.