HEADLESS
headless
(adjective) not having a head or formed without a head; “the headless horseman”; “brads are headless nails”
brainless, headless
(adjective) not using intelligence
Source: WordNet® 3.1
Etymology
Adjective
headless (not comparable)
Without a head; decapitated.
Without leadership.
(linguistics, of a phrase or compound) Not having a head morpheme or word.
(computing) Running without a graphical user interface; running without any attached output device (e.g, monitor) or input device (e.g, keyboard, mouse).
(of beer) Without a head of foam.
(obsolete) Heedless.
Source: Wiktionary
Head"less, a. Etym: [AS. heáfodleás.]
1. Having no head; beheaded; as, a headless body, neck, or carcass.
2. Destitute of a chief or leader. Sir W. Raleigh.
3. Destitute of understanding or prudence; foolish; rash; obstinate.
[Obs.]
Witless headiness in judging or headless hardiness in condemning.
Spenser.
Source: Webster’s Unabridged Dictionary 1913 Edition