ASININE
asinine, fatuous, inane
(adjective) extremely silly or stupid
Source: WordNet® 3.1
Etymology
Adjective
asinine (comparative more asinine, superlative most asinine)
very foolish; failing to exercise intelligence or judgment or rationality
Synonyms: foolish, obstinate
of, pertaining to, or characteristic of donkeys
Synonym: donkeyish
Source: Wiktionary
As"i*nine, a. Etym: [L. asininus, fr. asinus ass. See Ass.]
Definition: Of or belonging to, or having the qualities of, the ass, as
stupidity and obstinacy. "Asinine nature." B. Jonson. "Asinine
feast." Milton.
Source: Webster’s Unabridged Dictionary 1913 Edition