We found one dictionary that defines the word long as one's arm:

General (1 matching dictionary)

1. long as one's arm: Wiktionary

Definitions from Wiktionary (long as one's arm) ▸ adjective:  (simile) Very long. ▸ Words similar to long as one's arm ▸ Usage examples for long as one's arm ▸ Idioms related to long as one's arm ▸ Wikipedia articles (New!) ▸ Popular nouns described by long as one's arm ▸ Words that often appear near long as one's arm ▸ Rhymes of long as one's arm ▸ Invented words related to long as one's arm