Learn English – where does the word ‘satst’ get used? and what does it mean really

For your first point I found words such as hemeral and circadian, though there are more concept centered around a 24-hour period, but simply using the word day, as suggested by @FX_ would be the way to go, although ambiguous, but there doesn't seems to be another "English" word which would fit the bill.

On the second point, you have the word solidary, but also solidarily, which is an adverb defined as "showing solidarity". As such, we can safely assume that solidary is the adjective for the same concept.

EDIT: As for the fact that solidary against sympathetic, sympathetic comes from the Latin sympatheticus and sympathy has its own Latin words sympathia, both of each having Ancient Greek origin (sympathetikos and sympatheia), while both solidary and solidarity comes from the French solidaire which itself comes from the french word solide which has its roots in the Latin solidus, but this time not in the Greek.

"Can't hold their liquor" or "Can't handle their ale" are in common use in the UK.

Can't hold their drink/liquor

if someone can't hold their drink, they get drunk after drinking very little alcohol

www.idioms.thefreedictionary.com