zenki is "old" (89-90) chuki is "middle" (91-93) and kouki is "new" (97-99, not in the US), it denotes which style of a certian generation. they all have the same platform, just changes to that platform.
other terms? um, Onevia is a Silvia with a 180sx front (pop up lights). S14b(before) is 95-96, S14a(after) is 97-98.
what else do you have questions about? chassis codes....
a sileighty can be any 180 hatch with any silvia front end, be it s13/s14/s15, doesn't make a difference...I wanna see a s14 sileighty...I think that would look sick...I love the s14 front end, so masculine, so muscular hehe (i'm not gay.)