NOUNS: The gender of tricky words in Spanish 1

Masculine nouns ending in -a — A significant group of Spanish nouns end in -a but are masculine — many are of Greek origin or refer to topics/systems: el problema, el sistema, el programa, el mapa, el poema, el idioma, el clima, el día. Adjectives modifying these must be masculine: el problema es grave.

El agua, el arma — feminine nouns with el — Feminine nouns beginning with a stressed a- or ha- take el (not la) in the singular to avoid a clash of vowel sounds: el agua, el arma, el hacha, el alma. They are still feminine — adjectives agree in the feminine: el agua fría. The plural reverts to normal: las aguas.

La mano, la foto, la moto — feminine despite -o — A handful of common nouns ending in -o are feminine: la mano, la foto, la moto, la radio, la dínamo. The first three are especially important since they appear constantly. Don't be misled by the -o ending.