10. Compound nouns, formed by combining a verb and a noun, are also masculine: el salvavidas (life saver).

11. Feminine nouns that begin with stressed a or ha use a masculine article in the singular only (el agua),
   but remain feminine in every respect (el agua limpia, las aguas negras).

12. The meaning of some nouns changes according to their gender:

(money) el capital (short story) el cuento (future) el mañana (order → arrangement) el orden (policeman) el policía (the Pope) el Papa

vs.

la capital (city) la cuenta (check, bill) la mañana (morning) la orden (order → command) la policía (policeforce or policewoman) la papa (potato)