What is the term for a word like 'cleave' that means two things that are exactly contrary to each other?

Answer 1

I don't think there is one, but there ought to be. Let's coin one! How about "enantinym" (from the Greek for "contrary")

The term is typically called a contronym or an auto-antonym. There are actually subclasses of such terms.

There is the first class of contranyms are those where the word itself means itself and its opposite only because two words with different origins became similar over time (convergence). These are are called true homographs. Some examples include:

• Cleave - which can mean (1) to break apart / He cleaved the salt into blocks. AND (2) to attach to something else / The child cleaved tightly to his mother when he was scared.
• Inflammable - which can (1) highly combustible / This methane gas is inflammable. AND (2) resistant to combustion / Stone is inflammable.

There is a second class of contranyms which are those where the word originally meant one thing, but eventually developed a secondary meaning with equal use that is opposite to the original meaning. These are called polysemous contranyms. Some examples include:

• Bolt - which originally meant (1) to secure or fasten / He bolted the tent peg into the ground. BUT changed to (2) to depart quickly / He bolted from the room since he was late.
• Sanction - which originally meant (1) to allow / Entering the park is sanctioned with a park ranger. BUT changed to (2) to be punishable / The company was sanctioned for breaking the law.
  

There is a third class of contranyms that has arisen due to differences in dialect. There is no proper name for these contranyms. Some examples include:

• Table - which (1) in British English is to put a bill up for debate AND (2) in American English is to cease debate on a bill. However, in each dialect, there is no confusion over the meaning.

Answer 2

The term is typically called a contronym or an auto-antonym. There are actually subclasses of such terms.

There is the first class of contranyms are those where the word itself means itself and its opposite only because two words with different origins became similar over time (convergence). These are are called true homographs. Some examples include:

• Cleave - which can mean (1) to break apart / He cleaved the salt into blocks. AND (2) to attach to something else / The child cleaved tightly to his mother when he was scared.
• Inflammable - which can (1) highly combustible / This methane gas is inflammable. AND (2) resistant to combustion / Stone is inflammable.

There is a second class of contranyms which are those where the word originally meant one thing, but eventually developed a secondary meaning with equal use that is opposite to the original meaning. These are called polysemous contranyms. Some examples include:

• Bolt - which originally meant (1) to secure or fasten / He bolted the tent peg into the ground. BUT changed to (2) to depart quickly / He bolted from the room since he was late.
• Sanction - which originally meant (1) to allow / Entering the park is sanctioned with a park ranger. BUT changed to (2) to be punishable / The company was sanctioned for breaking the law.
  

There is a third class of contranyms that has arisen due to differences in dialect. There is no proper name for these contranyms. Some examples include:

• Table - which (1) in British English is to put a bill up for debate AND (2) in American English is to cease debate on a bill. However, in each dialect, there is no confusion over the meaning.

Answer 3

The term for a word like 'cleave' is "contronym" or "autoantonym." This refers to words that possess contradictory meanings.

Answer 4

I don't think there is one, but there ought to be. Let's coin one! How about "enantinym" (from the Greek for "contrary")