Sentence:  With a little manœuvring they contrived to meet on the doorstep which was […] in a boiling <WSD>stream</WSD> of passers-by, hurrying business people speeding past in a flurry of fumes and dust in the bright haze. 
Meaning of the word marked with <WSD> tags:  Any steady flow or succession of material, such as water, air, radio signal or words.