Or perhaps Cumulus Congestus! I have a great little book called The Cloud Collector's Handbook by Gavin Pretor-Pinney. I referred to it to see if your cloud is Cumulus Nimbus and it seems that C. Nimbus has ice crystals at its highest part, which gives a softened or fluffy effect. I don't know, it seems a rather vague sort of definition.
Whatever!!! It is a wonderful thing in the sky.