They both have the sense of singling out a discordant element.

The "however" meaning attaches to a word that can be translated as "but" in most languages, but the "only" meaning is specifically Germanic and is a relict of Saxon in the English language. Phrases like, " I have but one life to give for my country" are deliberately archaic in English. In Dutch, the however/only dichotomy is very much alive and well in the word "maar."

Hmm, not quite. "I got out of the bus but didn't come into the house right away" would be very awkward as "I got out of the bus except I didn't come into the house right away." Even the paperback novel version, "I got out of the bus all right. 'Cept I didn't come into the house right away," sounds like it's saying something different. There's an element of suspense there, an implication of "I did something unexpected at that point."

Somehow this all relates to the reason why the "however" meaning of the word "but" splits into two logically distinct words in Russian, "a" and "no," referred to by one website as "adversative and contrastive conjunctions." There is one logical "but" for unexpected things, and another for merely contrasting things. "I am older but no wiser," a purely contrastive phrase, probably defeats being rendered with "except." At least, "I am older except I am no wiser" is nonsensical.

Taka's original question relates to Mr Pedantic's example 4, 'we can but wait', i.e. 'we can only wait'.

I'm not sure that this is best defined as an ellipsis.

This construction can't stand on its own. It only exists as a response or a reaction:

1. 'What do we do now?' 'We can but wait.'

2. 'Thrash the boy soundly. He must be taught a lesson.' 'He is but a child, John!'

3. 'There but for the grace of God go I, thought Allingham, as the soldiers hustled the man away.'

In its full context, the adverbial 'but' is therefore a contrasting 'however':

1. 'What do we do now?' 'There is nothing to be done. However, we can wait.'

2. 'Thrash the boy soundly. He must be taught a lesson.' 'If he were old enough to know better, that would be reasonable. However, he is a child, and so it is not reasonable.'

3. 'The soldiers hustled the man away. "That might have happened to me", thought Allingham. "However, by the grace of God, it did not happen to me."'

Hello Taka

'But' derives from Old English 'butan', which originally meant 'outside',
'without', 'except'. It didn't develop its modern use as a conjunction
until the 13th century.

Chaucer (born 1340) uses 'but' extremely often in his Canterbury Tales.
As well as the conjunctive meanings, he uses 'but' in the sense of
'only'. He does this in two ways:

1. 'But' = 'only'

'I holde a mouses herte nat worth a leek
That hath but oon hole for to sterte to...' (Wife of Bath's Tale)

The significant portion here = 'That hath but oon hole', which =
'that has but one hole'.

2. 'But' preceded by a negative = 'only'

'Ey! for verray god, that nys but oon...' (Miller's Tale)

The significant portion here = 'that nys but oon'.

This would be translated into modern English as 'that is but one'.
However, it literally means 'that is not but one', since 'nys' =
'ne ys' = 'is not'.

Now the presence of 'nys' [i.e. 'ne ys'] is interesting. 'Ne', the Old
English negative, was originally used on its own to mean 'not'. Gradually,
perhaps because 'ne' seemed too weak, people began to reinforce it
with 'noht', which = 'not'. (The same thing happened in French,
where 'not' = 'ne...pas'.)

So for a time, like modern French, English used a double negative
form for a single negative sense. Then 'ne' dropped out of use,
in the 13th century, and 'not' assumed its modern role.

'Nys' in Chaucer thus presumably points to the older usage, which in
this example would have been the equivalent of 'that is not but one'.

Which means we can say that in Chaucer's time, both 'but' and 'not but'
could be used for 'only' (i.e. 'we can but wait' and 'we can not but wait'
would have meant the same thing).

In other words, over time, a negative has dropped out of a grammatical
construction without changing the meaning.

So to return to your original question:

'We can only wait' =
'We can but wait' =
'We can not but wait' =
'We can not do but we can wait' =
'We can do nothing except wait'.

Which takes us back to 'except' and the Old English 'butan'.

MrP