propeller

Propeller is simply propel plus the agent suffix -er, marking 'the thing that does the propelling.' That -er traces back through Old English -ere to Proto-Germanic *-ārijaz, which itself borrowed from Latin -ārius, a suffix used to form nouns of agent or occupation.

There's no dramatic shift in meaning here — the word has always meant 'thing that propels,' built straightforwardly once 'propel' existed as a verb in English.

The -er ending links propeller to countless other English agent nouns formed the same way, since -er descends from the same Old English -ere suffix.