cilia and flagella
"You could say that cilia and flagella are like synonyms, they have almost the same meaning (and structure), although they are two different things."
A very good blog this is...
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.