Not even: 〜すら

X すら means “even X”: X is the extreme case, the most basic or the most unexpected, which shows how serious the situation is. Very often with a negative (名前すら知らない). For a subject, you say ですら (専門家ですら). すら is more written and literary than さえ, and isn't used in the condition 〜さえ〜ば. Written register.

• 彼は隣の人の名前すら知らない。かれはとなりのひとのなまえすらしらない。He doesn't even know his neighbour's name.
• この問題は、専門家ですら解くのが難しい。このもんだいは、せんもんかですらとくのがむずかしい。This problem is hard to solve, even for specialists.
• 疲れ果てて、立ち上がる力すら残っていなかった。つかれはてて、たちあがるちからすらのこっていなかった。I was exhausted: I didn't even have the strength left to stand up.

すら marks the limiting case: if even X is affected, then everything else is all the more so. 名前すら知らない = he doesn't even know the name, so as for the rest… It's an emphatic word, often tinged with surprise or reproach.

• 隣の人の名前すら知らない。となりのひとのなまえすらしらない。He doesn't even know his neighbour's name.
• 当時は、電話をかけることすら簡単ではなかった。とうじは、でんわをかけることすらかんたんではなかった。In those days, even making a phone call wasn't easy.

すら replaces が and を, but is added after other particles. For the subject, ですら is readily used. A verb is nominalised with こと.

• この悩みは、親にすら打ち明けられなかった。このなやみは、おやにすらうちあけられなかった。I couldn't even confide this worry to my parents.

In the sense of “even”, すら and さえ are almost interchangeable; すら is more written. But さえ has a second use that すら lacks: the minimal condition 〜さえ〜ば (“as long as”). You say 時間さえあれば, never “時間すらあれば”.

• お金さえあれば、何でもできると思うのは間違いだ。おかねさえあれば、なんでもできるとおもうのはまちがいだ。Thinking that money alone lets you do anything is a mistake.

も is the neutral form (一度も). さえ is common in speech and writing. すら is more written. だに is literary and fixed (夢にだに思わない). The higher you go, the more formal the register.

• 彼とは一度も話したことがない。かれとはいちどもはなしたことがない。I've never once spoken to him.