Sentence:  For <WSD>want</WSD> of a nail the shoe was lost. / For <WSD>want</WSD> of a shoe the horse was lost. / For <WSD>want</WSD> of a horse the rider was lost. / For <WSD>want</WSD> of a rider the battle was lost. / For <WSD>want</WSD> of a battle the kingdom was lost. / And all for the <WSD>want</WSD> of a horseshoe nail. 
Meaning of the word marked with <WSD> tags:  Lack, absence.