When the word came to mind today, I realized it must be a dying word, because even the infantry in modern armies is mechanized, and do very little marching, except as physical training. Our army flies to places of conflict, or gets there by naval transport. So I looked up stragglers in my Merriam-Webster's Collegiate Dictionary, Tenth Edition. It didn't even get its own entry, but was reduced to being appended to the verb straggle, as its noun form. The definition made no mention of armies:
straggle vi straggled: straggling 1. to wander from the direct course or way: ROVE, STRAY 2. to trail off from others of its kind (little cabins
Next I looked in a more comprehensive dictionary, the Shorter Oxford English Dictionary, where straggler still had its own entry:
straggler noun 1. A person who straggles; spec. (a) a person who strays away from or trails behind a main body, esp. on a line of march; . . . . .
So ordinary dictionaries have relegated the word to obsolescence, and only the extraordinary dictionaries keep this barbarous relic of the past in their repertoire. It's not a bad thing that stragglers are a relic of the past, of course. But for those of us who like to learn from history, it's good to know the OED is still there to define the terms the modern world has left behind.
Postscript: To give some idea of the numbers of stragglers a failed campaign can have, here is Wikipedia's description of Napoleon's retreat from Russia:
It [the Grande Armée] reached its maximum size of 600,000 men at the start of the invasion of Russia in 1812. All contingents were commanded by French generals, except for a Polish and an Austrian corps. The huge multinational army marched slowly eastwards, with the Russians falling back before it. After the capture of Smolensk and victory in the Battle of Borodino, Napoleon and a large part of the Grande Armée reached Moscow on 14 September 1812; however, the army was already drastically reduced in numbers due to bloody battles with Russians, disease (principally typhus) and long communication lines. The army spent a month in Moscow, but was ultimately forced to march back westwards. Assailed by cold, starvation and disease, and constantly harassed by Cossacks and Russian irregulars, the retreat utterly destroyed the Grande Armée as a fighting force. As many as 400,000 died in the adventure and only a few tens of thousands of ravaged troops returned.