THANK Definition & Meaning – Merriam-Webster

The meaning of THANK is to express gratitude to —used in the phrase thank you usually without a subject to politely express gratitude or sometimes to emphasize a preceding statement especially by implying that it is not subject to question —used in such phrases as thank God, thank goodness usually without a subject to express gratitude or more often only the speaker’s or writer’s pleasure …

 https://www.merriam-webster.com/dictionary/thank