Seemingly from in- +‎ decus, decor- (compare dēgener from genus, gener-). Functionally a variant of indecōrus.

• (Classical Latin) IPA^(key):
• (modern Italianate Ecclesiastical) IPA^(key):

indecor (genitive indecoris); third-declension one-termination adjective

1. alternative form of indecōrus
   • 29 BCE – 19 BCE, Virgil, Aeneid 7.231:

     Nōn erimus rēgno‿indecorēs, nec vestra ferētur

     (please add an English translation of this quotation)

   • 29 BCE – 19 BCE, Virgil, Aeneid 11.423:

     Tempestās), cūr indecorēs in līmine prīmo

     (please add an English translation of this quotation)

   • 29 BCE – 19 BCE, Virgil, Aeneid 11.845:

     Nōn tamen indecorem tua tē rēgīna relīquit

     (please add an English translation of this quotation)

   • 29 BCE – 19 BCE, Virgil, Aeneid 12.25:

     Nec genus indecorēs. Sine me‿haec haud mollia fātu

     (please add an English translation of this quotation)

   • 29 BCE – 19 BCE, Virgil, Aeneid 12.679:

     Morte patī, neque me‿indecorem, germāna, vidēbis

     (please add an English translation of this quotation)

Rare and mostly used in poetry. Note that the more common indecōrus cannot be used in dactylic meters because it contains a long-short-long syllable sequence. Servius the grammarian, observing that most masculine nouns ending in -or form a genitive singular in -ōris (with long -ō-), supposes that this word might lack a nominative singular. As an alternative to this, some dictionaries hypothesize a two-termination nominative singular, indecoris/indecore.

Third-declension one-termination adjective (non-i-stem).

• “indecor”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
• indecor in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.