L'appendiabiti is the singular form, gli appenditiabiti is its plural. This word doesn't change, what changes are the articles! For the singular form we use L' because it starts with a vowel and for the plural we use the article "gli" because of the same reason!
"i" is used before the masculine plural words starting with a consonant! (for example: i sogni, i giochi, i cuori)
But there are many exceptions: Gli is also used with words starting with Z, SC, SCH, SQ, GN,
(Gli zaini, gli scoiattoli, gli squali, gli schiavi, gli gnomi,)
For the feminine plural words we ALWAYS use LE. (le Amiche, le Mamme, le SCatole, le Zebre, le Anatre)
