"st" suffix

What is the meaning and origin of the 'st' suffix in the following words:

midst, amidst, unbeknownst, amongst....etc.


How are these words with the suffix different from the words, mid, amid, unbeknown, among and the like?

Paulo, The meaning of the suffix is nil. It is just an alteration of the -s suffix used for adverbs (cf 'toward' & 'towards'). They mean exactly the same as the other words that lack it, except for 'mid' and 'midst'.

'Mid' and 'midst' are different, though related, words. Both come from the 'amid'/'amidst' complex, but 'mid' and 'midst' are not used interchangeably.

The only other instance I know of where there is a difference of meaning is in 'again' vs. 'against'