Something that is convivial is friendly and agreeable, or festive. Convivial is a warm and social term; it's most often used to talk about gatherings of people who are in high spirits and enjoying one another's company, often sharing in a meal or refreshments. Its gregarious nature makes sense given its origin: convivial comes from the Latin noun meaning "feast." When describing a person, convivial means "merry company, jovial." Convivial is good company any time of year, but given its appetite for feasting and gathering, it's no wonder we hear convivial a little more around the holidays!
Cold describes anything or anyone with a relatively low temperature. People can feel cold on a brisk and breezy day. Beverages can be cold, too, which is usually a good thing! Nippy does not work for people or beverages; this snappy adjective is usually used to describe chilly weather. This term entered English describing things that nip or bite, giving us the association of a sharp or biting cold. Like a nippy dog, a nippy wind may snap at your nose or fingers!
To corroborate something is to make more certain of it with evidence. In a courtroom, witnesses might be called to corroborate a story put forth by a defendant. Early findings in scientific research might be corroborated by additional scholarly work or laboratory results. More broadly, corroborate means “to strengthen”—and since this term's debut in English in the first half of the 16th century, it has been used to refer to strengthening or reinforcing things materially, to strengthening the health of things or people, and to strengthening a claim or statement.