† laˈssationObs. [n. of action f. L. lassāre: see lassate a.] Relaxation; weariness. 1650Charleton Paradoxes 139 The Imagination in this life is not onely subject to lassation.1669W. Simpson Hydrol. Chym. 97 The animal spirits are..wearied and willingly give themselves up to a lassation.