To enclose or encase completely with or as if with a covering: "Accompanying the darkness, a stillness envelops the city"(Curtis Wilkie).
To attack (an enemy's flank).
[Middle English envolupen, to be involved in, from Old French envoluper, envoloper : en-, in; see en-1 + voloper, to wrap up.] en·vel'op·er n., en·vel'op·ment n.