Under the Old Oak Tree
To corroborate is to confirm what someone else has asserted. You strengthen his or her statement, argument, or stance by shoring it up with your own. In the 16th century, corroborate simply meant to strengthen something material. Its source was the Latin word roborare, to make strong.
An early cousin was roborant, an invigorating or strengthening medicine. So was roboration, a strengthening, support, or invigoration. The old forms roborean and roboreous open another window into the roots of the word: both mean pertaining to oak.
In Latin, robus was the name for an oak tree.
The variant root -robur- shows up in a few words, mostly obsolete. Roburite is a flameless explosive of very high power. Roburnean means of or belonging to oak. Robur-oak is a very hard-wooded variety of oak.
All of this explains our word robust, which is used for everything from a healthy body to a strong cup of coffee.
SIDEBAR: facts about oak trees
(substitute @ for AT above)