From sub- (prefix meaning ‘beneath, under’) +‎ glacial (“of or relating to glaciers; cold and icy; (figurative) very slow”).^[1][2]

• (Received Pronunciation) IPA^(key): /sʌbˈɡleɪ.ʃl̩/, /sʌbˈɡleɪ.ʃɪ.əl/

• Audio (Southern England):

  (file)

• (General American) IPA^(key): /ˌsʌbˈɡleɪ.ʃ(ə)l/
• Rhymes: -eɪʃəl
• Hyphenation: sub‧gla‧ci‧al

subglacial (not comparable)

1. Formed or occurring beneath a glacier or other body of ice.

   Antonym: supraglacial

   • 1836 September 2, J. R., “Art. VI. Observations on the Causes which Occasion the Variation of Temperature between Spring and River Water.”, in J[ohn] C[laudius] Loudon, editor, The Magazine of Natural History, and Journal of Zoology, Botany, Mineralogy, Geology, and Meteorology, volume IX, number 66, London: […] [Andrew Spottiswoode] for Longman, Rees, Orme, Brown, Green, and Longman,[…], published October 1836, →OCLC, page 534:

     These streams continue to flow in winter as well as in summer, although in less quantity; […] It is also this melting beneath the ice (subglacial, suppose we call it) which loosens the ice from the ground, and occasions, or rather permits, the perpetual downward movement, with which "The glacier's cold and restless mass / Moves onward day by day."

2. (hyperbolic, informal) Moving at a rate allegedly slower than a glacier; extremely slow.

   Synonyms: glacial; see also Thesaurus:slow

   Antonyms: see Thesaurus:speedy

   • 2020 September 23, Nigel Harris, “Comment: We MUST Seize the Moment”, in Rail, Peterborough, Cambridgeshire: Bauer Media, →ISSN, →OCLC, page 3:

     Securing political approval for even modest changes to railway organisation and structure has been of sub-glacial speed and complexity since 2004, when Government abolished the Strategic Rail Authority and put itself in charge.

sub- +‎ glacial

• IPA^(key): /subɡlaˈθjal/ [suβ̞.ɣ̞laˈθjal] (Equatorial Guinea, Spain)
• IPA^(key): /subɡlaˈsjal/ [suβ̞.ɣ̞laˈsjal] (Latin America, Philippines)
• Rhymes: -al
• Syllabification: sub‧gla‧cial

subglacial m or f (masculine and feminine plural subglaciales)

1. subglacial