Once per turn (monster card effects)

Can "Legendary Six Samurai - Shi En's" effect be activated during you're opponents turn?

http://yugioh.wikia.com/wiki/Legendary_Six_Samurai_-_Shi_En

For example my opponent has a "Legendary Six Samurai - Shi En" on the field and I activate "pot of avarice" during my turn. Can he negate it? My opponent said he could negate it and I lost the duel because of this.

I need a clear definition of monster cards that have "once per turn" effects

Shi En can activate in either players turn because it is a quick effect, aka spell speed 2.

So "Legendary Six Samurai - Shi En" is not an ignition effect card?

If so what exactly is an ignition effect card?

http://yugioh.wikia.com/wiki/Ignition_Monster_Effects

The reason why Shi En's effect is NOT an ignition effect because you can activate it in response to another effect. Ignition effects can only be activated during your turn and cannot be activated as chain link 2 or higher.
Examples of Ignition effects include Hand of the Six Samurai and Legendary Six Samurai - Mizuho

GoldenEyes wrote:Can "Legendary Six Samurai - Shi En's" effect be activated during you're opponents turn?

http://yugioh.wikia.com/wiki/Legendary_Six_Samurai_-_Shi_En

For example my opponent has a "Legendary Six Samurai - Shi En" on the field and I activate "pot of avarice" during my turn. Can he negate it? My opponent said he could negate it and I lost the duel because of this.

I need a clear definition of monster cards that have "once per turn" effects

Once per turn, when your opponent activates a Spell/Trap Card, you can negate its activation and destroy it. If this face-up card on the field would be destroyed, you can destroy another face-up "Six Samurai" monster you control instead.

Yes, you can. The effect is totally clear, if not the effect could say:

Once during each of your turns, you can select and activate 1 of the following effects:
● Select 1 monster on the field, and remove it from play. If you activate this effect, this card cannot attack during this turn.
● If this card destroyed your opponent's monster by battle, it can attack once again in a row.

It is only a example, the effect of Black Luster Soldier. I almost forgot, the rulling of Legendary Six Samurai-Shi-en:

* It can be activated during each player's turn.

Source: http://yugioh.wikia.com/wiki/Card_Rulings:Legendary_Six_Samurai_-_Shi_En