New Delhi, Oct. 25 -- PARIS - France's private sector shrank again in October, and the contraction pulled the rest of the euro zone's momentum down with it.

The S&P Global Flash Eurozone Composite PMI Output Index fell to 51.9 from 53.1 in September, its weakest reading in four months and well short of the 52.7 economists had expected. Anything above 50 signals growth, so the bloc is still expanding. But the pace has now cooled to the slowest of the current four-month run, and the services and manufacturing gauges both missed forecasts, as Euronews reported in its analysis of the survey.

France supplied most of the damage. Its composite index dropped to 48.4 from 51.1, against a forecast of 50.5, which undid the one-month return to grow...