We found one dictionary that defines the word underpack:

General (1 matching dictionary)

1. underpack: Wiktionary

Definitions from Wiktionary (underpack) ▸ verb:  (intransitive) To pack too little. ▸ Words similar to underpack ▸ Usage examples for underpack ▸ Idioms related to underpack ▸ Wikipedia articles (New!) ▸ Words that often appear near underpack ▸ Rhymes of underpack ▸ Invented words related to underpack