The Romulan concept of honor-- Defined as such in the glossary of The Romulan Way...

Mnhei'sahe--The Ruling Passion: a concept or concept-complex which rules most of Rihannsu life in terms of honor. Mnhei'sahe is primarily occupied with courtesy to people around one: this courtesy, depending on circumstances, may require killing a person to do him honor, or severely disadvantaging one's self on his behalf. There are ramifications too involved to go into, but generally, mnhei'sahe is satisfied if all the parties to an agreement or situation feel that their "face" or honor is intact after a social (or other) transaction. NB: the concept has been occasionally mistranslated as implying that a given action is done "for a person's good." This is incorrect: such a concept literally does not exist in Rihannsu. One does things for one's own good-- or rather, the good of one's honor-- and if properly carried out, the actions in question will have benefitted the other parties in the transaction as well.

Enterprise linguist Lieutenant Janice Kerasus described mnhei'sahe as such, "...not quite honor-- not quite loyalty-- and not quite anger or hatred or about fifty other things. It can be a form of hatred that requires you to give your last drop of water to a thirsty enemy-- or an act of love that requires you to kill a friend." (TOS novel: My Enemy, My Ally)