Without a chief; lacking a leader or having no one in authority; leaderless.
Formed from 'chief' plus the suffix '-less,' which creates adjectives meaning 'without' (like 'harmless,' 'hopeless,' 'careless'). The pattern is ancient and highly productive in English.
The '-less' suffix is one of the most productive suffixes in English—you can add it to almost any noun to mean 'without that thing,' which is why even rare words like 'chiefless' are instantly understandable even if you've never seen them before.
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