Made white or pale (adjective); briefly boiled and then cooled in ice water, usually vegetables (verb past tense).
From Old French 'blanchir' meaning to make white, from 'blanc' (white). The cooking technique preserves this 'whitening' sense in the pale appearance of blanched vegetables.
When you blanch broccoli, you're using the exact same word that describes a person going pale with fear—both literally mean to turn white, which is why cooks and poets use the same word.
Complete word intelligence in one call. Free tier — 50 lookups/day.