the.com/spinelessness

means A lack of the backbone needed to stand up, object, or act when it actually matters.

from Built from 'spine' (the backbone, via Latin 'spina' meaning thorn or prickle, since vertebrae looked thorny to anatomists) plus '-less' and '-ness.' The literal spine became a metaphor for courage and resolve sometime before the 19th century — the idea being that without that inner rod, a person just folds. 'Spineless' as an insult for cowardice is the older, punchier form; 'spinelessness' is simply its abstract noun, the condition of having none.