cosign / cosine are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
cosign: (verb) sign and endorse (another person's signature), as for a loan.
cosine: (noun) ratio of the adjacent side to the hypotenuse of a right-angled triangle.
cosign: NA
cosine: NA
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)