1. To writhe, flail, or fling around wildly, violently, or uncontrollably. One of the cables came loose in the wind and lashed about across the deck of the boat. The toddler started lashing about in the midst of his tantrum.

2. To swing or flail something around wildly, violently, or uncontrollably. In this usage, a noun or pronoun is used between "lash" and "about." The lion tamer lashed his whip about to impress the audience. The wind lashed the flag about all night long, but it never came unfixed from the flagpole.