Sentence:  "I was passing by," he began to stammer, trembling with his <WSD>diffidence</WSD>, "I—happened to be passing along this way, and so—er—as I was passing this way, I says to myself, says I, 'I'll just stop into the shop a minute.' 
Meaning of the word marked with <WSD> tags:  The state of being diffident, timid or shy; reticence or self-effacement.