Few studies have been previously carried out in relation to the variations in the definitions of specialized terminology. This paper aims to contribute to the analysis of lexicographical entries that the Spanish academic and general dictionaries have considered according to four pairs of terms belonging to the genres of the extrajudicial field: (1) arbitration and arbitrator; (2) conciliation and conciliator; (3) negotiation and negotiator; and (4) mediation and mediator. For this purpose, a diachronic perspective is adopted and, at the same time, a comparative point of view by reviewing the definitions that specialized glossaries provide is chosen. Finally, the lexical-semantic analysis allows to trace an evolutionary line in the meaning of these terms and to strengthen the links between the sciences of language and law.Few studies have been previously carried out in relation to the variations in the definitions of specialized terminology. This paper aims to contribute to the analysis of lexicographical entries that the Spanish academic and general dictionaries have considered according to four pairs of terms belonging to the genres of the extrajudicial field: (1) arbitration and arbitrator; (2) conciliation and conciliator; (3) negotiation and negotiator; and (4) mediation and mediator. For this purpose, a diachronic perspective is adopted and, at the same time, a comparative point of view by reviewing the definitions that specialized glossaries provide is chosen. Finally, the lexical-semantic analysis allows to trace an evolutionary line in the meaning of these terms and to strengthen the links between the sciences of language and law.Existem poucas referências para o estudo das variações na definição da terminologia especializada. O presente artigo tem por objetivo contribuir para a análise das entradas lexicográficas que aparecem no dicionário da Real Academia da Língua Espanhola em diferentes épocas e sobre quatro pares: (1) arbitragem e árbitro, (2) conciliação e conciliador, (3) negociação e negociador; e (4) mediação e mediador. Para este fim, uma perspectiva diacrônica é adotada e, ao mesmo tempo, as definições são comparadas a partir de outra série de glossários, neste caso, de especialidade jurídica. Por fim, a análise léxico-semântica permite estabelecer uma história do significado dos termos ereforça os laços entre as ciências da linguagem e da lei
