Equivocation

What it is

Uses a word in two different senses within one argument so that the conclusion seems to follow.

Example "A feather is light; what is light cannot be dark; so a feather cannot be dark."

Framing effect bias
Choosing words with a different emotional colour shifts a conclusion, which is the framing effect.
Motte-and-bailey fallacy
The motte and the bailey are often joined by an ambiguous word that means a modest thing in one place and a bold thing in the other.
Weasel words fallacy
Both depend on language doing hidden work: equivocation by shifting meaning, weasel words by staying vague.
Continuum fallacy fallacy
Continuum arguments exploit vague terms, much as equivocation exploits ambiguous ones.
Amphiboly fallacy
Equivocation shifts the meaning of a word, amphiboly the meaning of a whole sentence's grammar.