The words collaborate and corroborate don't fall under the category of homophones (see last post), but people do confuse them on occasion. This confusion causes more problems in speaking than in writing, which makes me think the misattributions are more a slip of the tongue than an actual lack of knowledge. Sometimes people substitute a less frequently used word under the assumption that it makes them sound smarter. Sometimes people don't even recognize that there is a distinction.
Regardless of why they are confused, it's easy to separate the two words, despite their similarities. How are they similar? Both are transitive verbs that form nouns the same way (the verb collaborate turns into the noun collaboration, and the verb corroborate turns into the noun corroboration), and they both have to do with working together in some capacity.
How are these words different, then?
Collaborate means to work together. For example (shameless plug here), my mother and I collaborated on Pizza Friday. Lennon and McCartney formed one of the most successful musical collaborations of all time.
On the other hand, corroborate means to confirm or give support to a statement, theory or finding. Your doctor might use corroborate this way: "The tests corroborated my diagnosis." A detective might say, "Fingerprint evidence corroborated the witness's testimony that you were in the apartment."
Looking at the history of a word can help clarify meaning. I love to explore the roots of words both because I can get a more precise definition and often expand my vocabulary in the process of seeing other related words. Remember, I was an English major, and I take my fun where I can get it!
The root of collaborate is "laborere-" (to labor). In addition to the word labor, other words that come from the same root include elaborate and laborious.
The word corroborate comes from the root "robor-" (strength). Another word that comes from this same root is robust.
The bottom line: To collaborate is to labor or work together. To corroborate is to provide strength, um, evidence.
If you have pairs of words that you'd like to learn more about, please let me know. Happy Sunday!