Underside/ˈʌndərsaɪd/ Definition 1 of 2Pro Tip 1/3Physical Literalness Refers to the actual bottom side of an object you can touch. They found a signature on the underside of the sculpture. Pro Tip 2/3Tangible Details Often used to describe specific details not immediately visible. She examined the underside of the leaf for insects. Pro Tip 3/3Hidden Area Used to identify parts usually not seen or considered. Mechanics check the underside of cars for rust and damage.