bad deed / sin / evil
Feminine adjective used as noun. From the root س-و-أ (to be bad). Plural: سَيِّئَاتٌ. Paired with حَسَنَة in many verses.
God's justice: bad deeds are only counted once (1:1 ratio), while good deeds are multiplied - a Quranic expression of divine mercy exceeding justice.