The act of maintaining a bro-like persona via the intake of sunlight.* This can be witnessed on Beaches and college campuses across the United states. (note: also possible around fires, at Dave Matthews concerts, etc.) Specifically occurs with men ages 18-24, "chill" (see chill) outside in small groups, or "crews". (note: sunglasses, vintage tees, sandals, and Abercrombie and Fitch paraphenalia are key indicators of brotosynthesis.) Common, less scientific, synonyms include but are not limited to the following: chillin', hangin, livin' the dream.
*Recent studies indicate that the intake of cheap beer may aid in this process; it has not yet been confirmed.
1. "Dude work has sucked lately"
"Yeah fuck my job, too. This weekend we need some brotosynthesis."
2."Hey Gail, why doesn't Matthew Mcconaghey ever wear a shirt?"
"Well, Susan, because he's engaging in brotosynthesis"
3. "Yo break out the natty and meet me at the shore, we're gonna brotosynthesize."