Is a brown spider with cross on the back poisoness?

Something is poisonous if it makes you sick when you eat it. Something is venomous if it makes you sick when it stings you or injects venom through a fang.

Almost all Spiders have one kind of venom or another. Almost no spiders have enough venom to kill a healthy adult human, however, there are lots of spiders that have enough venom to make you hurt for a while. There are only two main kinds of spiders that you really have to worry about (particularly if you have kids) in the U.S. They are:

•Black widow spiders

•Brown recluse spiders

Neither one of these spiders fits the description you give.