Excellent question which certainly preoccupies philosophers. It's good step on the path of better critical thinking, so keep at it!
The relation between natural language ambiguity and equivocation
First, as Conifold in the comments points out, equivocation is an informal fallacy whereby one uses two different meanings of the word when drawing an inference. This means that there must be a persuasive argument present. From the WP article:
Since only man [human] is rational,
and no woman is a man [male],
therefore, no woman is rational.
One has two premises that both appear to be about the same category (man), but actually move from the category "human" to "male" to draw the conclusion. The ambiguity in language (does "man" mean human? male? tough guy?) makes the fallacy possible. Because this is a problem in natural language, sometimes we use more formal languages. Philosophers, scientists, and mathematicians, for example, work hard to avoid ambiguity by presenting special types of definition. This is one way we can more be confident we know what words "mean".
Definitions, meaning, and language use
As to the second part, what you are doing is engaging in skepticism, which is an attitude towards belief and knowledge such that you are doubting. This is a very popular philosophical practice that goes back at least to the Ancient Greeks and is studied in philosophy in the field of epistemology. The meaning of words is also studied by philosophers of language and linguists. There are a few schools of thinking on semantics, that is meaning. A famous philosopher named Ludwig Wittgenstein pointed out that a word like "game" seems to share meanings that work like family resemblance. Some words don't seem to be defined very easily!
Philosophy and Science of Meaning
Philosophers have always asked about language, but philosophers of language have been heavily influenced by the science of linguistics which studies particular aspects of language such as phonology and grammar as well as how the brain works. Today, they can be broadly sorted into a traditional view on language and a more recent movement called cognitive semantics. Thinkers such as Noam Chomsky, Charles Fillmore, and Eleanor Rosch have solved some of the mysteries of language. Aristotle established the traditional view called definitional structure which uses necessity and sufficiency to establish word meanings. Cognitive semanticists argue that these are special cases, and that word meanings are largely contextual and prototypical. Ultimately, philosophers are still sorting out these issues of syntax and semantics using the latest in scientific techniques.
See Also
Since words are defined in terms of other words in dictionaries, leading to infinite loops, does it mean natural languages are meaningless?
Language and Philosophy
Is there a point to arguing about the meaning of words?
