requiring effort or concentration; complex and not easy to answer or solve; "raised serious objections to the proposal"; "the plan has a serious flaw"
of great consequence; "marriage is a serious matter"
concerned with work or important matters rather than play or trivialities; "a serious student of history"; "a serious attempt to learn to ski"; "gave me a serious look"; "a serious young man"; "are you serious or joking?"; "Don't be so serious!"
make (alcohol) unfit for drinking without impairing usefulness for other purposes
modify (as a native protein) especially by heat, acid, alkali, or ultraviolet radiation so that all of the original properties are removed or diminished
add nonfissionable material to (fissionable material) so as to make unsuitable for use in an atomic bomb