by Foggy Brume, Ian Tullis, and Meta Group B
Answer: RADIO

Like with the prefix "atm-" each of these words is a prefix for one of the five layers of the atmosphere without the "-osphere" part, plus one letter. These can be placed in atmospheric order and their extra letters extracted:

• REX = EX- + R
• THE RAM = THERM- + A
• MEDS = MES- + D
• STRAIT = STRAT- + I
• TROOP = TROP- + O

for the answer RADIO.