When a reader of Spain's premier daily, El País, wrote to reproach an ungrammatical usage, she exclaimed: "If only Lázaro Carreter were still around." But he was, and when he quoted the correspondent in his next column, one could sense his relish at being cited as the yardstick for correct Spanish. Emeritus Professor Fernando Lázaro Carreter, who has died aged 80, was a keen monitor of the mass media and its use of language, a subject on which he wrote with formidable erudition and mordant wit.

He headed the language's governing body, the Real Academia Española (RAE) from 1991 to 1998. Like his fellow academician Emilio Lorenzo (obituary, 10 July 2002), Lázaro saw the Spanish vocabulary absorbing influences from without and everyday speech learning nuances and malapropisms from talkshow hosts, football commentators or pompous politicians.

Although he leaves a hundred-odd learned monographs in philology and literary criticism, his best-known work was a long series of newspaper columns on the way the language of his adored Cervantes was mutating into what he called a form of "neoespañol". Appearing first in ABC, then in El País, these acerbic essays were collected as El dardo en la palabra (A Dart to the Word, 1997; A Fresh Dart, 2003) and have sold nearly half a million copies. So much for don Fernando's fear that the Spanish public did not care about the degradation of their language.

Born in Zaragoza, Lázaro was educated in the city's Instituto Goya and enrolled first in Zaragoza University, graduating in 1945 from the Complutense in Madrid where he stayed to complete a doctorate in Romance languages. He lectured there until 1949 when - at just 26 - he won a chair in linguistics and literary criticism at Salamanca University. He loved Salamanca, later becoming its dean of philosophy and letters. In 1972 he moved to the Autonomous University of Madrid and was elected to the RAE. He returned to the Complutense for the last decade of his university career, retiring in 1988.

He was twice elected head of the illustrious Academy. Internationally, he was one of the most renowned Hispanists of his age, addressing conferences in Britain, Italy, Japan and Latin America, earning visiting professorships in Austin (Texas), Heidelberg, the Sorbonne and Toulouse and being awarded too many honorary degrees, literary prizes and decorations to catalogue here.

The literature of the 16th, 17th and 18th centuries was his forte; he was a world authority on Góngora, Lope de Vega, Menéndez Pelayo and Quevedo, among others. At the RAE, he led the creation of enormous new databases of Spanish usage and re-edited the standard school dictionary. His RAE became less of an aristocratic ornament and more of an organic protagonist in Spanish culture.

His erudition was leavened with a sense of humour that had something of the P.G. Wodehouse or Flann O'Brien about it. Sloppy or pretentious writing amused him as much as it irked him. He would nail a reporter to the wall for tautologically referring to a "humanitarian disaster", for misusing the word "ethnic" or reporting that "a third per cent of voters abstained". A radio report that "a bus pulled up and six people disembarked from the latter" prompted him to wonder what kind of circumlocutions people might routinely employ in ten years' time. He imagined someone arriving home: "I could have sworn I put the key in my jacket pocket, but I can't find the aforementioned in the latter."

Lázaro Carreter would have rejoiced in the missionary success of Lynne Truss with Eats, Shoots and Leaves - he had been there and done that for his own beautiful language. He savoured every change in its flavour, unerringly shot his darts at its misuses and has left it healthier than he found it. His bullshit radar was always finely tuned; when he found the language fattening in expression but shrinking in meaning, with words being robbed of their meaning. phrases used flabbily or entire verbs being pensioned off, he protested.

His essential message was universal: that journalists, politicians, broadcasters and all who make their living from words have a duty as guardians of the use of language. Interviewed for his 80th birthday, he was asked whether he despaired of present-day Spain. He replied: "This is the only Spain I have." ["No tengo otra."]

Fernando Lázaro Carreter, linguist, critic and academician: born Zaragoza, 13 April 1923; married to Angelita Mora Salvo (two daughters, one son); died Madrid, 4 March 2003.