bright / light / shine

one, 1 / the first in order, foremost / the beginning / the best / a kind of; one of something / (card games) an ace / unity / the bottom string of a shamisen or other Japanese musical instrument

transplant rejection / allergic reaction

chain reaction (series of events) / chain reaction (type of nuclear reaction)

an overreaction

nuclear reaction

overreaction

each person

a research student (i.e. a visiting or non-matriculating graduate student) / a researcher

researcher