Not all Spanish nouns ending in a are feminine.

There are many examples of common Spanish nouns that end in a and are masculine. You need to take this into account when making them agree with articles and adjectives.
Note that many of these words are of Greek origin, some of which are technical or scientific.
muchos días maravillosos, (never
muchas días maravillosas), many wonderful days
Un programa exitoso (never una
programa exitosa), a successful program
Un problema extraordinario (never
una problema extraordinaria), an extraordinary problem
Un poema magnífico, a magnificent poem

Un mapa extenso (never una mapa
extensa), a large map
los planetas lejanos, far planets
el cometa, comet
el gran dilema, the big dilemma
el fonema, phoneme
el aroma, aroma
el panorama, panorama
el sistema, system
el morfema, morfeme (and many
other linguistic terms ending in -ma)
un tema divertido, a funny subject
(theme)
el enfisema, emphysema
el clima caluroso, hot weather
el edema, edema
el eczema, eczema (and many other
health related terms ending in -ema, -oma)
el crucigrama, crossword puzzle
el organigrama, organization
chart, flow chart
el fonograma, phonogram
el telegrama, telegram (and most
words ending in -rama)
Many nouns ending in -ista and referring to males are masculine. When they refer to
females, they take the corresponding feminine articles and adjectives, but the noun ending remains -ista. Note that many of these nouns correspond to the suffix -ist in English.
el taxista, taxi driver (la
taxista would the female taxi driver).
el analista, analyst
el comunista, communist
el laborista, Labor Party member
el anarquista, anarchist
el alquimista, alchemist
el columnista, columnist
(journalism)
un deportista, a sports person,
athlete
un conferencista, a lecturer
el periodista, journalist
el cronista, feature writer
el novelista, novelist
el cuentista, fiction writer
el rescatista, rescuer  (a
common word used in many countries but neglected by the RAE)
el socorrista, rescuer
el alpinista, mountain climber
el bañista, bather, swimmer
el recepcionista, receptionist
el dentista, dentist
el inversionista, investor
el paracaidista, paratrooper
el concertista, music performer
el anestesista, anesthetist
el especialista, specialist
el tenista, tennis player
el velocista, runner, sprinter
el ajedrecista, chess player
el golfista, golf player
el basquetbolista, basketball
player
el clavadista, diver
el beisbolista, baseball player
el contrabandista, smuggler
el extremista, extremist
el racista, racist
el narcisista, narcissist
el antagonista, antagonist
el oficinista, office clerk
el manicurista, manicurist (note
that this word is related to la mano,
hand)
el pedicurista, pedicurist (note
that this word is related to el pie,
foot)
el machista, male chauvinist
el maquillista, make up specialist
el estilista, hairdresser
el especialista, specialist
el adventista, Adventist
el artista, artist
el retratista, portrait artist
el caricaturista, cartoonist
el turista, tourist
el arreglista, music composer,
arranger
el pianista, pianist
el baterista, drummer
el trompetista, trumpeter
el organista, organist
el violinista, violinist
el acordionista, accordionist
el guitarrista, guitarist
el malabarista, juggler
el maquinista, a person working on
a train locomotive
el transportista, a person working
in transportation
Watch out:
Not all -ist English nouns have -ista Spanish counterparts:
anthropologist, el antrop�logo (not antropologista).
Here are some more nouns
el policía, policeman (la polic�a,
police department or police woman)
el guardia, guard
el atleta, athlete
el espía, spy
el poeta famoso, a famous poet
el cura, priest
el sofá, sofa
el tequila, tequila
el vigía, watchman
Originally published on 20060712. Update: 20061206. Latest update 20210603 (spanishNY.com)