Mano

Short for Hermano, which means brother in Spanish.

Slang for good friend or person you have known a while and bonded with ( Mano - male ) ( mana - female ) originated from the Spanish slang of hermano (brother) someone you are close to. Popular between 2 people that originate from seperate countries. I.e Britain and Spain

An expression used to show deep love, usually used for cute & adorable people. Frequently used by love-birds to express how they feel towards each other.

The term is Spanish and literally means "Hand to Hand" as in unarmed combat. However in its modern incarnation the term is used in any scenario where two (usually male) individuals are going to have some sort of competition. Eg Darts, Snooker, an actual fight, even videogames. It is rarely a serious threat.

A Portuguese expression to describe a fight between two people

mano a mano; mano mano; man mano

As far as Italians are concerned these expressions (freely exchangeable) have only one use and meaning, the origin of which - most likely - has to do with the way in old times people used to measure short distances by using an open hand.
You put a hand widely open beside another end moving on as you take measures. From this habit in old times may have arisen the idea of following an event - shal we say - "step-by-step" (if you're measuring long distances) ... or similarly "hand-by-hand" (if you're measuring, say, a cloth or a stick of wood, etc.).
By extension, every time an Italian wants to mean following something very closely and at every new event uses this expression.
I mark on the wall my child's height as (mano a mano) he grows.

This expression could come either from italian or spanish, it literally means "hand to hand" and it is used to indicate an argue, a verbal fight between two people.