They go by either name John. My father would always use the term lag bolt so that must have stuck in the memory. Maybe a regional term, boulon de l'entraîneur in your neck of the woods?
In Sandy’s situation I’d recommend pre-drilling a hole and using a large flat washer with each bolt to spread the load when tightening up with a suitable socket. A couple of 5” bolts should do assuming it’s a 2” joist and a 4” newel - if smaller than that drop to a 4” bolt. The hardest part of the job would be getting access in the first place and having enough space between the joists to get a drill in.