i Register
In some senses, backboneless is marked as figuratively, literally. Watch for register when choosing this word.
adj
Without a backbone; invertebrate.
Once, like a drunken man, I lurched forward, and fell upon my knees. Such was my backboneless state that for some seconds I remained where I was, half disposed to let things slide, accept the good the gods had sent me, and make a night of it just there.
Cowardly, spineless.