Well guys my question or topic is not that hard, i just want to make sure. Hope i get the answer im looking for

the arachnophobia achievment says "outrun" a gigantic threat in the city it does not say "defeat" or something similar, my concern is that if we get to fight it!!! not only run from it :/ wanted to know if someone knows if we get to fight it and kill it or just escape from it..... it would svck by tango to not put the huge monster to confront and just run from it.

No one has played the full game yet, so no one can answer your question until the game has been released.
And if it's a boss fight or something similar, Bethesda and Tango are likely keeping it a secret.

There could be multiple encounters with the spider, or it could just be how they decided to word the achievement.
But if all you have is a handgun, how are you supposed to fight a giant spider anyway? Running might be the only way survival would be plausible.
Remember, this is a Survival Horror game, not something like Dark Souls or Zelda where boss fights are essential to the experience.

Many games have giant spiders to kill, so I hope the encounter is something new and fresh.

Judging by numerous trailers players will be running away a lot from different foes.....however we don't know will we actually fight them. This is getting in to a bad trend when devs force the tension by making player unable to confront enemy. Let's Hope TEW does it all right)

But as Pluto said it could be a numerous encouters with the same boss wich will eventually end up by defeating it.

Yep, it all depends on the arsenal at hand. Even with the shotgun it seems kinda silly to kill a giant monster... if anything shooting at it seems kind of a lame way to kill it. I'd like to see some traps and use of the level itself to defeat that thing...

can't wait