Some languages distinguish between the time period from dawn to dusk (when the sun is up) and the time period from midnight to midnight (i.e. 24 hours). I'm not sure but I think one of the two terms usually has a broader meaning and can be used to express both. So perhaps there are three 'categories':
dawn to dusk | midnight to midnight | both
[flag=]en[/flag] day | day | day
[flag=]sv[/flag] dag | dygn | dag
[flag=]de[/flag] Tag | Tag | Tag
[flag=]ru[/flag] день | сутки | день
[flag=]et[/flag] päev | ööpäev ("night-day") | päev
[flag=]mhr[/flag] кече | кече | кече
[flag=]myv[/flag] чи | чи-ве ("day-night") | чи