How many letters does the top answer for “a document giving an official instruction or command” have?

The most common answer is authorization (13 letters).

Crossword clue: a document giving an official instruction or command

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

authorization 13 letters wn-def

a document giving an official instruction or command

mandate 7 letters wn-def

a document giving an official instruction or command