"Out-sides" is a compound word that refers to the exterior or outer surfaces of an object or entity. Its antonyms would, therefore, be related to the inner or interior side. Some of the antonyms for out-sides include insides, interiors, undersides, underneath, beneath, inner face, inner part, hidden part, and internal aspect. These words describe the opposite of out-sides and indicate that the focus is on the inward-facing aspects of the object or entity. By utilizing these antonyms, writers and speakers can provide greater clarity and specificity to their descriptions and convey a more complete picture of the subject at hand.