surface has 13 distinct synonyms spread across 6 of its 10 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its 2 recorded opposites are subsurface, overhead.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the outer boundary of an artifact or a material layer constituting or resembling such a boundary
“there is a special cleaner for these surfaces”
the extended two-dimensional outer boundary of a three-dimensional object
“they skimmed over the surface of the water”
the outermost level of the land or sea
“earthquakes originate far below the surface”
a superficial aspect as opposed to the real nature of something
“it was not what it appeared to be on the surface”
information that has become public
“all the reports were out in the open”
a device that provides reactive force when in motion relative to the surrounding air; can lift or control a plane in flight
on the surface
“surface materials of the moon”
Synonyms, antonyms and the broader and narrower relations for surface come from Princeton University’s WordNet. Full sources and licences.