form has 47 distinct synonyms spread across 17 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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 phonological or orthographic sound or appearance of a word that can be used to describe or identify something
“the inflected forms of a word can be represented by a stem and a list of inflections to be attached”
any spatial attributes (especially as defined by outline)
“he could barely make out their shapes”
the spatial arrangement of something as distinct from its substance
“geometry is the mathematical science of shape”
the visual appearance of something or someone
“the delicate cast of his features”
a printed document with spaces in which to write
“he filled out his tax form”
(biology) a group of organisms within a species that differ in trivial ways from similar groups
“a new strain of microorganisms”
an arrangement of the elements in a composition or discourse
“the essay was in the form of a dialogue”
a particular mode in which something is manifested
“his resentment took the form of extreme hostility”
(physical chemistry) a distinct state of matter in a system; matter that is identical in chemical composition and physical state and separated from other material by the phase boundary
“the reaction occurs in the liquid phase of the system”
an ability to perform well
“he was at the top of his form”
a mold for setting concrete
“they built elaborate forms for pouring the foundation”
to compose or represent
“This wall forms the background of the stage setting”
develop into a distinctive entity
“our plans began to take shape”
assume a form or shape
“the water formed little beads”
Synonyms, antonyms and the broader and narrower relations for form come from Princeton University’s WordNet. Full sources and licences.