Sentence:  By a remarkable analysis of what he called Churchill's "peculiar gift of overwriting and <WSD>underspeaking</WSD>," Burton also managed to leave us — as after one of Sir Winston's own speeches — with a feeling of love and of thanks for the privilege of living in the same age with Churchill. 
Meaning of the word marked with <WSD> tags:  To fail to say enough; to be too taciturn.