| firmly | categóricamente |
| firmness | resolución |
| Firmus | Firmo II |
| firmware | firmware |
| Firouzabad | Firuzabad |
| first | antes |
| First Age | Primera Edad del Sol |
| first aid | primeros auxilios |
| first aid kit | botiquín |
| First Aid Station | casa de socorro |
| First Alcibiades | Primer Alcibíades |
| First Anglo-Afghan War | Primera Guerra Anglo-Afgana |
| First ascent | Primera ascensión |
| First Austrian Republic | I República de Austria |
| First Balkan War | Primera Guerra de los Balcanes |
| First Barbary War | Guerra de Trípoli |
| First Battle of Bull Run | Primera batalla de Bull Run |
| First Battle of St Albans | Primera batalla de San Albano |
| First Battle of Tapae | Primera batalla de Tapae |
| First Battle of the Aisne | Batalla de Axona |
| First Battle of the Marne | Batalla del Marne |
| First Boer War | Guerras de los Bóer |
| First Brazilian astronaut accompanies ISS replacements | Primer astronauta brasileño viaja hacia la Estación Espacial Internacional |
| First Carlist War | Primera Guerra Carlista |
| First Certificate in English | First Certificate in English |
| First Chechen War | Primera Guerra Chechena |
| first class | primera clase |
| First Coalition | Primera Coalición |
| First Comics | First comics |
| First Communion | Primera comunión |
| First Congo War | Primera Guerra del Congo |
| First Congress of Rastatt | Tratado de Rastatt |
| First contact | Primer contacto |
| First Council of Constantinople | Primer Concilio de Constantinopla |
| First Council of Lyon | Concilio de Lyon I |
| First Council of Nicaea | Concilio de Nicea I |
| First Council of the Lateran | Concilio de Letrán I |
| first course | entremés |
| first cousin once removed | sobrino segundo |
| First Crusade | Primera Cruzada |
| first day cover | sobre de primer día |
| First Day of My Life | First day of my life |
| First dynasty of Egypt | Dinastía I de Egipto |
| First earthlike planet discovered outside solar system | Descubren un planeta habitable |
| First Empire | Primer Imperio Francés |
| First Employment Contract | Ley de Contrato del Primer Empleo de Francia |
| First Epistle of Clement | Primera epístola de Clemente |
| First Epistle of John | Primera epístola de Juan |
| First Epistle of Peter | Primera epístola de Pedro |
| First Epistle to the Corinthians | Primera epístola a los corintios |
| First Epistle to the Thessalonians | Primera epístola a los tesalonicenses |
| First Epistle to Timothy | Primera epístola a Timoteo |
| First face transplant performed on French woman | Realizan en Francia el primer transplante de rostro |
| first floor | planta baja |
| First Folio | First Folio |
| First French Empire | Primer Imperio Francés |
| First Impressions of Earth | First Impressions of Earth |
| First Indochina War | Guerra de Indochina |
| First Intermediate Period of Egypt | Primer periodo intermedio de Egipto |
| First International | Primera Internacional |
| First Jewish-Roman War | Primera Guerra Judeo-Romana |
| first lady | primera dama |
| First language | Lengua materna |
| First League of Serbia and Montenegro | Meridijan Superliga |
| FIRST Lego League | FIRST Lego League |
| First Liberian Civil War | Primera Guerra Civil Liberiana |
| first lieutenant | alférez |
| First meeting | Toma de contacto |
| First Minister | First Minister |
