vacillating

Vacillating between silly and serious, the talk with Ansari is interrupted several times with giggling—most of it his own.

Vacillating and unintelligent, his actions were all guided by his mistress, Mme Bonnemain.

Yet the feeling is in most children weak and vacillating, and is wont to be mixed with other and less noble ones.

To go back on it, and at the eleventh hour, would proclaim him weak and vacillating, and the effect might be as Strachan said.