IPA: /ðɛrˈæt/
KK: /ðɛrˈæt/
In relation to a specific event or place that has been mentioned.
The committee will meet thereat to discuss the new policy.
Thereat is formed from "there" (from Old English "þær", meaning at that place) and "at" (meaning in that location or position). The word "thereat" means at that place or location, indicating a specific point in relation to something mentioned.
Think of 'there' as pointing to a specific place and 'at' as indicating a position — together, they help you remember that 'thereat' refers to being at that specific location.