tandem

Tandem comes from Latin tandem, meaning 'at last, at length, finally,' built from tam ('so, to such an extent') plus the demonstrative suffix -dem. English speakers borrowed it as a joke, using 'at length' to describe horses harnessed one behind the other in a line instead of side by side.

What began as a pun on a Latin adverb of time settled into English as a straightforward noun for horses (and later bicycles) arranged in a single line, with the adjective, adverb, and verb forms all growing out of that noun.

Tandem's story stays with its own Latin roots, tam and -dem.