acrus

Reassignment of Classical Latin ācer from the third declension to the first/second, facilitated by the fact that the nominative singular form ācer can itself be taken as a second declension form, initially yielding a paradigm ā̆cer, ā̆cra, ā̆crum (compare Classical Latin niger, nigra, nigrum).[1] The wide distribution of its descendants across the branches of Romance implies its presence in the oral language considerably predates its appearance in writing.[1]

• (Proto-Romance) IPA^(key): /ˈakrʊs/

ā̆crus (feminine ā̆cra, neuter ā̆crum); first/second-declension adjective (Vulgar Latin)[2]

1. (proscribed) sour, bitter
   • 3rd–4th century C.E., Appendix Probi:

     acre non acrum

     [Say or write] acre, not acrum.