"Consciousness is a fascinating but elusive phenomenon. Nothing worth reading has been written about it."
Stuart Sutherland in the 1989 International Dictionary of Psychology
The definition of 'consciousness' is a matter of some debate. Most people - and probably even most philosophers - use the layperson definition of the term being equivalent to subjective mental experience.
Personally, I disagree with this common and popular definition. It seems terribly imprecise and fails to differentiate between related terms of sentience, sapience etc. It requires additional distinctions such as described by Ned Block between “phenomenal consciousness” (P-consciousness) of pure experience, sounds, emotions etc., and “access consciousness” (A-awareness) of introspection, memory etc.
An alternative is where consciousness is distinguished from sentience (from the Latin “to feel”) and sapience (Latin “to know”, or “to be wise”). "Consciousness" derives from Latin conscientia which primarily means moral conscience (knowledge-with, shared knowledge, cf., Cicero).
Descartes was the first to use it in the sense of the individual ego and awareness and that's probably where we get the lay usage today, but even that was expanded by Locke to include moral responsibility.
Consciousness is typically described in terms of phenomenological subjectivity; awareness, a sense of self, which is also applied in contemporary medicine as a continuum (from being fully alert and cognisant to being disorientated, to being in delirium, to being unconscious and unresponsive). The historical definition suggested social co-knowledge (con- "together" + scire "to know") suggesting moral reasoning (conscientia, conscience) and language. This original use is still applied in law with the concept of legal responsibility with consciousness.
Lest there is any confusion; sentience = the ability to feel (from the Latin "to feel"), sapience = the ability of awareness ("to be wise"), consciousness = shared knowledge (con - 'together', scientia - 'to know').
Using these more precise (and etymologically accurate) definitions, consciousness and language are strongly related to the point of being occurring simultaneously. One becomes conscious at the same time that they grasp the shared (c.f., Wittgenstein) symbolic values.
It is worth reading the material of the contemporary linguistic pragmatistsm particularly Jurgen Habermas, and Karl-Otto Apel for further consideration of this point of view.