How many letters does the top answer for “watch over or shield from danger or harm; protect” have?

The most common answer is guard (5 letters).

Crossword clue: watch over or shield from danger or harm; protect

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

guard 5 letters wn-def

a person who keeps watch over something or someone

ward 4 letters wn-def

a person who is under the protection or in the custody of another