1630s, "internal knowledge," from conscious + -ness. Meaning "state of being aware of what passes in one's own mind" is from 1670s; meaning "state of being aware" of anything is from 1746. Consciousness-raising is attested from 1968.
he lost consciousness
his sudden consciousness of the problem he faced
conscience
conscient
conscientious
conscionable
conscious
consciousness
conscript
conscription
consecrate
consecration
consecution