BLESS is to receive the kindness of God upon a person.
Jesus commands repented persons “BLESS and CURSE NOT” (Romans 12:14, Matthew 5:43-48).
BLESS is, also, to speak kind things about God, to God, and about God’s holy things (Preachers are holy things, The Holy Bible, Church are a few examples).
The opposite of blessing God is blaspheming — Him or his holy things. (Rom 2:24, 2Tim 3:2, Titus 2:5, James 2:7, Rev 13:6)