Morphologically hid +‎ -en.

• enPR: hĭdʹn, IPA^(key): /ˈhɪd(ə)n/
• (Canada) IPA^(key): /ˈhɪdn/

• Audio (US):

  (file)

• Rhymes: -ɪdən

hidden

1. past participle of hide

hidden (comparative more hidden, superlative most hidden)

1. Located or positioned out of sight; not visually apparent.

   hidden treasure; hidden talents

   • 1892, James Yoxall, The Lonely Pyramid, chapter 7:

     It was the Lost Oasis, the Oasis of the vision in the sand. […] Deep-hidden in the hollow, beneath the cliffs, it lay; and round it the happy verdure spread for many a rood.

   • 2014 June 14, “It's a gas”, in The Economist, volume 411, number 8891:

     One of the hidden glories of Victorian engineering is proper drains. Isolating a city’s effluent and shipping it away in underground sewers has probably saved more lives than any medical procedure except vaccination.

2. Obscure. (Can we add an example for this sense?)

• See Thesaurus:hidden

• See Thesaurus:hidden

hidden (plural hiddens)

1. (crosswording) A hidden answer clue; one in which the letters of the solution appear consecutively in the wordplay.
   • 1975, Games & Puzzles:

     Hiddens are indicated thus; (e.g.) Grow (maraudinG ROWdies).

   • 1987, The Listener:

     The two types of clue which everyone should aim to solve at first reading are anagrams and hiddens.

   • 2020 August 20, Telegraph Media Group Ltd, The Telegraph: How To Solve a Cryptic Crossword: Mastering cryptic crosswords made easy, Hachette UK, →ISBN, page 3:

     16 of the 30 clues in this puzzle are hiddens; these are asterisked.

From Middle High German hüeten, from Old High German huoten, from Proto-West Germanic *hōdijan.

• IPA^(key): /ˈhiden/, [ˈhidən]
• Rhymes: -idən

hidden (third-person singular present hitt, past participle gehitt, auxiliary verb hunn)

1. (transitive) to tend, to mind, to look after