(n.) a solemn promise; an engagement to be wed
Troth-plight is a long-forgotten word defined by the Oxford English Dictionary as “a betrothal”, or “a solemn promise or engagement, especially of marriage”.
No prizes for working out that troth-plight is related to the somewhat old-fashioned expression to plight one’s troth. But there are a few questions floating around here. Like, isn’t a plight a perilous situation? What does that have to do with marriage proposals? And what on earth is a troth?
Let’s start with plight. As a word for a bad or risky situation, plight is a thirteenth century word with etymological ties, via French, to the Latin verb plicare, meaning “to fold”. Originally, this plight meant simply “condition” or “state”—in the sense that events have “unfolded” to get us to the “state” we’re currently in.
This plight was initially a fairly neutral term, which could refer to either a good or bad state of affairs. That was, at least, until the word began to develop a predominantly negative connotation in the late Middle English period, to leave us with a word meaning “a perilous, intractable situation” today. Where did this negative meaning come from? Oddly enough, from the plight that actually concerns us here.
Long before we adopted that perilous plight from French, English had a plight of its own. The Anglo-Saxon word pliht meant “risk”, “damage”, or “danger”, while as a verb it could be used to mean “to place in danger” or “to compromise”. But by the Middle English period, this plight had changed too: as a noun, it was now beginning to be used to refer pledges or promises made despite the fact that they involved some manner of risk or potential for loss, while as a verb it meant “to give in pledge”, or “to put at risk of forfeiture”. And marriage proposals—somewhat unromantically—came under that umbrella.
Long story short, as a verb the plight of plight one’s troth essentially means “pledge”—and is related to the plight we use to mean “a dangerous situation” as it was once necessary to “pledge” to enter into or assist in risky situations.
As for troth, it’s simply another form of truth. Strictly speaking, in fact, it’s an example of what linguists call a “doublet”—a word (or rather, pair of words) that despite having phonological or orthographic differences (i.e. despite being spelled or pronounced differently) are etymological twins. In that sense, both troth and truth come from the Old English treowth, but while truth established itself as the dominant form, troth survived only in a handful of English dialects and in stock words and phrases like betrothal and to plight one’s troth.
From those two roots, the word troth-plight emerged in the Middle English period as a noun (“a betrothal”), a verb (“to engage to marry”), and an adjective (“bound by a promise or engagement”)—any sense of which suits the events of this week.