They communicate our thoughts, our ideas, our emotions. Choosing the precise word for the exact meaning is important.

Definitions of words and their origins are equally important. Especially when you don't know what they mean, although a quick search using your favourite search engine will resolve any uncertainty about the meaning of a word.

That wasn't always the case. There was time when dictionaries didn't exist or were limited in their scope.

The Professor and The Madman takes us back to such a time: the middle of the 19th century. The University of Oxford Press tasks Dr James Murray (Mel Gibson) with compiling a definitive dictionary of every known word and phrase in the English language.

Murray is determined to provide the origins, definitions and phrases from literary works across every century for each word.

The task soon becomes overwhelming. It impacts on his relationship with his wife and family. There is also resistance from the stodgy, conservative dons at Oxford, who mostly want him to fail. Even though they themselves have failed to produce a dictionary despite trying for decades.

Assistance in the compilation of the dictionary comes from an unlikely source. Dr William Minor, an American Civil War surgeon suffering post-traumatic stress disorder, answers Murray's call for assistance from ordinary citizens.

Minor is meticulous in his research and prolific in his submissions. He sends Murray 10,000 fully annotated entries. All are accurate with appropriate sources, origins and references.

There's a slight problem. Minor is an inmate at Broadmoor Criminal Lunatic Asylum. He has visions of a dead soldier pursuing him with the intention of killing him.

The intricacies of the story involve the wife of a man Minor murdered, the discomfort between Murray and his wife Ada, the politics within Oxford University Press, the jealousies and enmities between scholars, experimental medical procedures that brutalise the inmates and the humane guard Mr Muncie.

The lexicographic connection between Murray and Minor is substantial on its own. Attempting to define all the other complex relationships spreads the drama thinly. Each is a full movie on its own.

The Professor and The Madman exudes emotions: love, hate, fury, madness, and passion, professional and personal. In its final phase, the movie heads into melodramatic territory.

Not bad for a film about words and dictionaries.

Mel Gibson and Sean Penn are intense actors. Equal co-billing with the actors should go to the crinigerous stars of the movie.

Crinigerous? Don't know what that means? Consult your copy of the Oxford English dictionary. Or the Australian Macquarie dictionary. Or even your Funk and Wagnalls. Because words matter.