The most common and most likely answer to this crossword clue is the 6 letter word LORICA
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The straight part
We know that "What protected front of old" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what protected front of old = lorica.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LORICA mean?
LORICA noun- A cuirass, originally of leather, afterward of plates of metal or horn sewed on linen or the like.
- Lute for protecting vessels from the fire.
- The protective case or shell of a Loricifera, infusorian or rotifer