Definition of "astern"

After we had row'd, or rather driven about a League and a Half, as we reckon'd it, a raging Wave, Mountain-like, came rowling a-stern of us, and plainly bad us expect the Coup-de-Grace.

1719 May 6 (Gregorian calendar), [Daniel Defoe], The Life and Strange Surprizing Adventures of Robinson Crusoe, […], 3rd edition, London: […] W[illiam] Taylor […], published 1719, page 50

When we first espied the Dutch fleet sailing towards us, our whole blue squadron was astern much farther from us, so that Prince Rupert thought it absolutely necessary to slacken sail that they might have time to join us.

1838, M. Guizot, edited by J. Stuart Wortley, Memoirs of George Monk, Duke of Albemarle, London: Richard Bentley, page 307

Every yachtsman knows that if the ballast of a ship be too afore or too astern.

1872, Hunt's Yachting Magazine‎, volume 21, page 288

The chief engineer's evidence of the S.S. Lennox was the best given; but, as will be seen, he asserted that from the orders he received the Lennox's course was more astern than ahead.

1883, Lieutenant J. Menteith Brebner, RETURN WRECKS AND CASUALTIES IN INDIAN WATERS‎, page 140

but when near Cape Palmas the wind will perhaps be more astern

1883, Alexander George Findlay, A Sailing Directory for the Ethiopic Or South Atlantic Ocean‎

The galley fire was lighted; coffee was boiled; the sun shone brightly, and the ship astern was coming up fast.

1901, W. Clark Russell, The Ship's Adventure, Westminster: Archibald Constable, page 304

The steamer was more than ahead of us, just on our quarter as we say, and the light was more astern.

1966, Peter Padfield, The Titanic and the Californian‎, page 233