linearis

• (Classical Latin) IPA^(key): [liː.neˈaː.rɪs]
• (modern Italianate Ecclesiastical) IPA^(key): [li.neˈaː.ris]

From līnea (“line”) + -āris. Doublet of līneālis.

The post-Classical sense of "having the form of a line" is likely a back-formation(Can this⁽⁺⁾ etymology be sourced?) from the adverbial form līneāriter (literally “using a line or lines”), which (along with līneāliter) was often used with verbs of motion, resulting in reanalysis as "like a line", from which follows the adjectival sense "line-like".

līneāris (neuter līneāre, adverb līneāriter); third-declension two-termination adjective

1. line-; lineal; consisting of lines; pertaining to lines

   Synonyms: līneālis, līneārius

   pictūra līneāris ― line painting

   līneāris ratiō ― geometry (literally, “line theory”)

   līneāris probātiō ― line-based proof

2. (Late Latin) linear; line-like; having the form of a line

Third-declension two-termination adjective.

• līniāris

• līneāriter

Inflected form of līneō.

līneāris

1. second-person singular present passive indicative of līneō

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