While I agree with various points in the thread to the point it may be a bit much to list every single one of them, I'd like to clarify what I meant earlier citing Samurai as a "pseudo tank".

When I define a tank, I define them by their access of crowd control abilities or alternate peeling abilities. In the case of Samurai, this means their access to stun [Mineuchi] and bind [Hyosetsu] as their available interuption/peeling tools. The fact it has [Hissatsu: Chiten] and lifesteal via [Oka] is just some level of tankiness. Jobs in this category for me are:
[Tank] Paladin, Warrior
[DPS] Samurai

Being "tanky" does not automatically define a tank, pseudo or real deal - being "tanky" while being a good DPS means you are essentially a Bruiser. You go in, do the hurt and either hold the ground or bail if you fail, but you have limited or no crowd control/peeling tools. Jobs in this category are:
[DPS] Dragoon, Reaper, Monk
[Tank] Dark Knight, Gunbreaker

Short: tanky =/= Tank, but a Tank generally is tanky.