In the literal sense, "conscientia" means knowledge-with, that is, shared knowledge. The word first appears in Latin juridical texts by writers such as Cicero. Here, conscientia is the knowledge that a witness has of the deed of someone else. René Descartes (1596–1650) is generally taken to be the first philosopher to use conscientia in a way that does not fit this traditional meaning. Descartes used conscientia the way modern speakers would use "conscience". In Search after Truth (Regulæ ad directionem ingenii ut et inquisitio veritatis per lumen naturale, Amsterdam 1701) he says "conscience or internal testimony" (conscientiâ, vel interno testimonio). The problem of definition
The dictionary definitions of the word consciousness extend through several centuries and reflect a range of seemingly related meanings, with some differences that have been controversial, such as the distinction between inward awareness and perception of the physical world, or the distinction between conscious and unconscious, or the notion of a "mental entity" or "mental activity" that is not physical. The common usage definitions of consciousness in Websters Third New International Dictionary (1966 edition, Volume 1, page 482) are as follows: 

awareness or perception of an inward psychological or spiritual fact;  intuitively perceived knowledge of something in ones inner self
inward awareness of an external object, state, or fact
concerned awareness; INTEREST, CONCERN—often used with an attributive noun [e.g.
class consciousness]
the state or activity that is characterized by sensation, emotion, volition, or thought;  mind in the broadest possible sense;  something in nature that is distinguished from the physical
the totality in psychology of sensations, perceptions, ideas, attitudes, and feelings of which an individual or a group is aware at any given time or within a particular time span—compare STREAM OF CONSCIOUSNESS
waking life (as that to which one returns after sleep, trance, fever) wherein all ones mental powers have returned . . . the part of mental life or psychic content in psychoanalysis that is immediately available to the ego—compare PRECONSCIOUS, UNCONSCIOUSThe Cambridge Dictionary defines consciousness as "the state of understanding and realizing something." The Oxford Living Dictionary defines consciousness as "The state of being aware of and responsive to ones surroundings. ", "A persons awareness or perception of something." and "The fact of awareness by the mind of itself and the world. "Philosophers have attempted to clarify technical distinctions by using a jargon of their own. The Routledge Encyclopedia of Philosophy in 1998 defines consciousness as follows:

Consciousness—Philosophers have used the term consciousness for four main topics: knowledge in general, intentionality, introspection (and the knowledge it specifically generates) and phenomenal experience... Something within ones mind is introspectively conscious just in case one introspects it (or is poised to do so). Introspection is often thought to deliver ones primary knowledge of ones mental life.