Headless means having no head, or having no leader. A headless statue, a headless chicken, a headless organisation.
The literal sense belongs to statues, ghosts and folklore — the Headless Horseman, the many headless ladies of English haunting. Running around like a headless chicken is the fixed simile for panic, and it comes from the fact that a decapitated bird really does keep moving. In computing, headless means running without a screen — a headless server — which is a precise technical use.
1adjectiveheadlessHaving no head.
“Only a headless statue remained in the ruined temple garden.”
2adjectiverunningRunning without a screen, of a computer.
“The server runs headless in a cupboard, and we control it from our laptops.”
headless is a state of lacking a head.
Old English heafodleas is head plus -less, and every Germanic language builds it the same way. The compound has been unchanged for over a thousand years.
Proto-Indo-European
*kap-
Old English
hēafodlēas — headless
Middle English
heedles
English, today
headless
From Middle English heedles, hevedles, from Old English hēafodlēas (“headless”), equivalent to head + -less. Cognate with Dutch hoofdloos (“headless”), Danish hovedløs (“headless”), Swedish huvudlös (“headless”), Icelandic höfuðlaus (“headless”). chefless.
Etymology from Wiktionary, CC BY-SA