Oppressive means cruelly heavy, in rule or in weather. An oppressive regime, oppressive heat, an oppressive silence.
The weather sense is not a metaphor so much as a parallel: both press down on you, which is exactly what the word means. Oppressive heat is heavy and humid rather than merely hot. Of rule it means unjustly harsh. Note oppress; and that the Latin means to press against.
1adjectiveunjustlyUnjustly harsh, of rule.
“People lived in fear under the oppressive regime, which jailed anyone who spoke out.”
2adjectiveoppressiveHeavy and stifling, of weather.
“The air was hot and oppressive, and everyone was waiting for the storm to break.”
Too few real examples of this word to estimate which sense is commonest.
oppressive is a quality of heaviness.
Latin
opprimere
Medieval Latin
oppressare — to press against, oppress
Old French
oppresser
Middle English
oppressen
English
oppress
English, today
oppressive
Built from
From oppress + -ive. oppress comes from Middle English oppressen, from Old French oppresser, from Medieval Latin oppressare (“to press against, oppress”), frequentative of Latin opprimere, past participle oppressus (“to press against, press together, oppress”), from ob (“against”) + premere, past participle pressus (“to press”); see press.
Etymology from Wiktionary, CC BY-SA