Part of Speech: Verb

Definition: to attack vigorously or violently; assault.

Source: Dictionary.com

Found in Pity me not because the light of day by Edna St. Vincent Millay line 10

“This have I known always: Love is no more/Than the wide blossom which the wind assails,…”

When I first read these lines, I thought assail had something to do with a sail boat. I was wrong. After looking up the word, I was able to understand what the speaking was saying. The speaker is stating in line ten that the wind assaults flowers when it blows, kind of the way love assaults the heart sometimes.