a persistent or desperate hope that is unlikely to be fulfilled, a faint hope, a ‘hope against hope’
On the face of it, this is a curious expression, because the adjective forlorn does not normally mean faint but miserable, lonely, forsaken or sad. The current sense of forlorn hope derives either from wordplay or from a misunderstanding of its etymology: the term originally denoted a band of soldiers chosen to spearhead an attack, many of whom would not survive. It is first recorded in An arithmetical warlike treatise named Stratioticos (first published in 1579), by Leonard and Thomas Digges:
To the Generall of the field it appertaineth, al the time of the battaile to giue order, when the skirmishers, or Forlorne Hope shall retyre, and to what places.
It was an adaptation of Dutch verloren hoop, lost troop, composed of verloren (past participle of the verb verliezen, to lose) and hoop, company (literally heap).
As the term implied that the soldiers selected for this troop had faint hope of success, the hope in forlorn hope was associated in English with hope in the sense of expectation. In Sarah and Hagar: or, Genesis the sixteenth Chapter opened, in XIX sermons (published in 1649), Josias Shute (1588-1643), Church of England clergyman, wrote:
Let us stand in awe, and sin not: for if we sin, upon a presumption that we shall conceal either our actions or persons from God, it is a forlorn hope; our iniquities will finde us out.
(It is interesting to note that Dutch has the following homonyms, of distinct origins: hoop, meaning heap, and hoop, meaning hope. It is therefore possible that verloren hoop was also the object of wordplay in Dutch.)
The Dutch phrase is identical to German verlorener Haufen, and similar to Dutch verloren kinderen and French enfants perdus, which both mean, literally, lost children (incidentally, the word infantry is based on Latin infans/infant-). In A Dictionarie of the French and English Tongues (1611), Randle Cotgrave wrote:
Enfans perdus. Perdus, in warre; (ordinarily) gentlemen of companies, reserued for, and exposed vnto, all desperate seruices.
Similarly, as one of the senses of forlorn was ‘lost’, ruined, doomed to destruction, English had the expressions forlorn boys, forlorn fellows, etc., in the sense of men who perform their duty at the imminent risk of their lives, as well as forlorn fort, a fort held at extreme risk.
The later sense of forlorn hope has in turn given an additional meaning to the adjective forlorn, that of unlikely to succeed or be fulfilled (when speaking of an aim or endeavour). For example, the following appeared in The London Gazette of 23th April 1918:
Commander Goodhart displayed extreme and heroic daring in attempting to escape from the submarine in order to save the lives of those remaining on board, and thoroughly realised the forlorn nature of his act.
The adjective forlorn is from Old English forloren, past participle of the verb forlēosan, to lose utterly, which gave rise to the obsolete verb forlese, to lose, forsake, destroy. In this Old English verb forlēosan, the prefix for- is an intensifier of the verb lēosan, meaning to lose.
This verb lēosan gave rise to the obsolete verb lese, and to the past participle lorn, which is now an adjective meaning forsaken or wretched. For example, in The Personal History, Adventures, Experience, and Observation of David Copperfield the Younger of Blunderstone Rookery (Which He Never Meant to Publish on Any Account), the English novelist Charles Dickens (1812-70) makes Mrs Gummidge say:
I know what I am. I know that I am a lone lorn creetur’, and not only that everythink goes contrairy with me, but that I go contrairy with everybody.
The adjective lovelorn means miserable because of unrequited love or unhappiness in love. It appears to have been coined by the English poet John Milton (1608-74) in A Maske presented at Ludlow Castle, 1634 (also known as Comus, a masque):
Sweete Echo, sweetest nymphe that liv’st vnseene
within thy ayrie shell
by slowe Meanders margent greene
and in the violett imbroderd vale
where the love-lorne nightingale
nightly to thee her sad song mourneth well.