An Etymological Dictionary of Astronomy and Astrophysics

Wide in extent from side to side.

Etymology (EN): M.E. bro(o)d, from O.E. brad; cf. O.N. breiðr, Du. breed, Ger. breit, Goth. brouþs.

Etymology (PE): Pahn “wide, broad,” from Mid.Pers. pah(a)n; Av. paθana- “broad, wide, spacious;” PIE root *pete- “to spread;” cf. L. patere “to be open,”
Gk. petannynai “to spread out,” petalon “a leaf.”