Evolution is defined ambiguously, and claims that it is fact are based on
the ambiguity. It is usually defined as "change in heritable
characteristics in a population over time" (often expressed as "change in
allele frequencies"), which everyone accepts as fact, but that does not
mean that macroevolution or common descent are fact.
Language tends to be ambiguous at times (e.g., the entry for the word "set"
covers more than twenty-two pages of the original Oxford English
Dictionary.) The word "evolution" is an unfortunate instance of that
ambiguity; it is used for the fact of biological change over time; as
shorthand for the theory of evolution, which encompasses a much
broader range of observations and ideas; and for change generally, in
any realm. The ambiguity can usually be resolved by the context in
which the word is used, at least by people who know something about
biological evolution.
Mixing contexts is indeed improper, and the fact of allele frequency
change, by itself, does not establish the theory of evolution.
The soundness of the theory of evolution does not rest on ambiguity.
On the contrary, scientific papers are written so other scientists can
tell what the authors are talking about; they must be as unambiguous as
possible. The evidence is overwhelming: evolution is not only a
theory; major aspects of it, such as common descent, are also facts.
Creationists sometimes misuse the ambiguity to their own advantage,
trying, for example, to include cosmological change as part of the
theory of evolution (Hovind n.d.). This is gross ignorance, deliberate
dishonesty, or both.
