The Holy Quran contains these two different words which are present in many verses. The Arabic word "SAMA", translated to english "Heaven" means the Sky/Space where the sun, the moon, planets, stars, galaxies, etc are present. In many places in the holy Quran, you will find the word Sama with the arabic word Ard (Earth), for eg, "samawati wal ardi... (heavens and the earth)".
The Arabic word "JANNAT" translated to english "Paradise" means the place built by Allah (s.w.t) for the righteous; the gardens beneath which the rivers flow. The place of eternal peace and desires. The opposite of the word Jahannam (Hell) is Jannat and not Sama.
Summarizing all above:
Arabic word English Meaning Opposite Sama / Samawat Heaven / Heavens Ard (Earth) Jannat Paradise (Garden) Jahannam (Hell) Ard Earth Sama (Heaven) Jahannam Hell Jannat (Paradise)