I know there are plenty of words that use the -st ending: wouldst, whilst, unbeknownst, etc. but I'm not really sure what it means to add an -st suffix to a word. What does it mean to add the suffix? How can I tell what words can take the -st suffix? Are there any modern words that can take the suffix and not have people look at me in a strange way?
Learn English – What does the -st word ending mean and is it used in any modern vocabulary
meaningsuffixesverbs
Best Answer
Your -st endings are two different grammatical animals. In wouldst it is the standard verb ending for the archaic second person singular familiar thou:
Unbeknownst, however, is another creature entirely, even among its peers.
Emerging in both British and North American print sources in the 1830’s, unbeknownst was originally a colloquialism coined on the pattern of much older words such as unawares (1530s) or always (early 13th c.), adding the etymologically intrusive final t of amongst, whilst, betwixt, etc. The s is a remnant of the genitive case, often used in Old and Middle English to form adverbs from nouns or adjectives.
The word also appears in an 1875 Sussex dialect dictionary, suggesting the usage is older than its first appearance in print:
Even so, the word is a likely candidate for the last coinage in English using the adverbial genitive.
The adverbial genitive, though no longer productive, is a feature especially common to West Germanic languages. It’s hiding in plain sight in many common English words: once, twice, sideways, backwards, forwards and the alternatives amongst, whilst more common to British usage.
This means that you can no longer form words using the adverbial genitive -s, and unless you’re in a Shakespearean play, you won’t be using the thou form of English verbs anytime soon.