Past tense of bolster; supported, strengthened, or reinforced something.
From Old English 'bolster' meaning a long pillow, used metaphorically to mean 'to support' since Middle English times.
The word 'bolster' comes from pillows because pillows literally support your head—it's one of the few metaphors where you can still see the physical object behind the abstract meaning.
Complete word intelligence in one call. Free tier — 50 lookups/day.