ground has 23 distinct synonyms spread across 13 of its 23 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 one recorded opposite is figure.
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.
confine or restrict to the ground
“After the accident, they grounded the plane and the pilot”
instruct someone in the fundamentals of a subject
throw to the ground in order to stop play and avoid being tackled behind the line of scrimmage
hit a groundball
“he grounded to the second baseman”
the solid part of the earth's surface
“the plane turned away from the sea and moved back over land”
Synonyms, antonyms and the broader and narrower relations for ground come from Princeton University’s WordNet. Full sources and licences.
a rational motive for a belief or action
“the reason that war was declared”
a relation that provides the foundation for something
“they were on a friendly footing”
a position to be won or defended in battle (or as if in battle)
“they gained ground step by step”
the part of a scene (or picture) that lies behind objects in the foreground
“he posed her against a background of rolling hills”
material in the top layer of the surface of the earth in which plants can grow (especially with reference to its quality or use)
“the land had never been plowed”
a connection between an electrical device and a large conducting body, such as the earth (which is taken to be at zero voltage)
(art) the surface (as a wall or canvas) prepared to take the paint for a painting
the first or preliminary coat of paint or size applied to a surface