Uncertain; the following possibilities have been suggested, though the etymons are all first attested later than the English word:^[1]

• From Irish smidiríní, smiodairíní (“smithereens”), from smiodar (“broken piece, fragment”) + -ín (suffix forming diminutive nouns) + -í (slender form of -aí (suffix forming plurals of some nouns)).
• From smithers (“fragment; atom”) infixed with -een (suffix forming diminutive nouns in Irish English).
• From Hiberno-English (Wexford) smaddereen, a variant of smattering (“small amount or number of something; shallow or superficial knowledge of a subject”).
• From Hiberno-English (Wexford) smithered, smashed

• (Received Pronunciation, Ireland) IPA^(key): /smɪðəˈɹiːnz/
• (General American) IPA^(key): /ˌsmɪðəˈɹinz/

• Audio (General American):

  (file)

• Rhymes: -iːnz
• Hyphenation: smi‧ther‧eens

smithereens pl (plural only) (rare singular smithereen)

1. (originally Ireland, informal) Fragments or splintered pieces; numerous tiny disconnected items.

   Synonyms: shards, shivereens, smithers

   The urn shattered into smithereens the moment it hit the ground.

   When the waiter dropped the platter, one smithereen struck him above the knee, and the four remaining smithereens scattered across the floor.

   • 2022 January 12, Benedict le Vay, “The heroes of Soham...”, in RAIL, number 948, page 42:

     However, something once happened on the railway there which showed the very best of mankind: heroism, duty, self-sacrifice and calm professionalism under terrible pressure. It is a story which gives us far, far better reasons for remembering this attractive little town, which without these heroes would have been blown to smithereens in a gigantic explosion. (Two railwaymen lost their lives in 1944 when a wagon in an ammunition train caught fire and blew up, an even worse disaster was averted however.)

• smithereens (disambiguation) on Wikipedia.Wikipedia

• intermeshes