Lacking courage, strength, or determination; unwilling to face difficult decisions or take firm action.
From 'spine' (from Latin 'spina,' literally a thorn or backbone) plus the suffix '-less' (without). Used metaphorically since at least the 1800s to describe weak character.
Calling someone 'spineless' is a brilliant metaphor because your spine is literally what holds you upright and supports your movement—without it you collapse. So calling someone spineless is saying they morally collapse when facing pressure, a perfect physical metaphor for moral weakness.
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