From sub- +‎ marginal.

submarginal (comparative more submarginal, superlative most submarginal)

1. Less than, or worse than, marginal. Not meeting even the minimum standard of quality.
   • 1996, Staughton Lynd, "We are All Leaders": The Alternative Unionism of the Early 1930s:

     Nutpicking, along with chicken cleaning and rag sorting, constituted the very bottom of the submarginal industries in St. Louis in the 1930s, and it was in these industries that African American women found sporadic employment.

2. (anatomy, zoology, botany) Below a margin.

submarginal (feminine submarginale, masculine plural submarginaux, feminine plural submarginales)

1. submarginal

• “submarginal”, in Trésor de la langue française informatisé [Digitized Treasury of the French Language], 2012

• IPA^(key): /submaɾxiˈnal/ [suβ̞.maɾ.xiˈnal]
• Rhymes: -al
• Syllabification: sub‧mar‧gi‧nal

submarginal m or f (masculine and feminine plural submarginales)

1. submarginal