From card +‎ board.

• (UK) IPA^(key): /ˈkɑːdbɔːd/
• (US) IPA^(key): /ˈkɑɹdˌbɔɹd/, /ˈkɑɹˌbɔɹd/

• Audio (US):

  (file)

• Rhymes: -ɑː(ɹ)dbɔː(ɹ)d

cardboard (countable and uncountable, plural cardboards)

1. A wood-based material resembling heavy paper, used in the manufacture of boxes, cartons and signs.
2. (figurative) Something flat or insubstantial.
   • 1980 February 9, Andrea Loewenstein, “James Baldwin and His Critics”, in Gay Community News, volume 7, number 28, page 10:

     In my experience, one of the most vital times in the life of a piece of fiction is when a character begins to speak, timidly and softly, in one's head. Honest and true books get written when the author feels free to coax and invite that character in. If the author's response to that small voice is instead to submit it to a test: "Are you: black/white/gay/straight/male/female/Christian/Jewish/old/young/politically correct" the character will probably turn around and leave or else turn into cardboard.

   • 2018 February 21, Jeff Pearlman, “Parkland students, ignore the idiots”, in CNN‎^[1]:

     According to these keyboard warriors, the young men and women who survived the shooting are part of a big hoax, are liars, are mere cardboard cutouts – “crisis actors” who roam the country looking for mass shootings from which to promote their anti-gun message – all being pushed forward by the giant liberal machine that is Hillary Clinton’s robot attack army.

• Despite widespread general use in English, the term cardboard is deprecated in commerce and industry as not adequately defining a specific product.^[1]

• paperboard

cardboard

1. Made of or resembling cardboard; (figurative) flat or flavorless.
   • 1868, Arthur William A'Beckett, “Painted Ships and Painted Oceans”, in The Tomahawk, page 114:

     The worst of the thing, however, is that the enormity, such as it is, happens to be of a very cardboard and tinsel character.

   • 1973, Journal of Black Poetry, number 17, page 27:

     The thing really looked quite cardboard.

   • 2008, Katya Hokanson, Writing at Russia's Border‎^[2], page 122:

     While Lensky’s character is quite cardboard, Onegin’s manipulations and lack of ability to call off the duel because he fears society’s jibes, Lensky’s youth and naivety, and Tatiana’s reaction to the duel lend the event its gravity.

   • Twentieth-Century Scottish Drama, page 501:

     MUMMER 3 pulls out an inflated cushion with a very cardboard crown on it.