Observe also: financier, friend, sieve.

708. Nouns ending in a vowel and -y form the plural by adding -s.

709. Verbs ending in a vowel and -y form the third person singular, present indicative, by adding -s.

710. Nouns ending in a consonant and -y form the plural by changing the -y to -i and adding -es.

711. Many nouns ending in -f or -fe form the plural in -ves.