expression
usually; ordinarily; in the past
Fixed polite expression used mainly in formal letters or speeches to refer to one's usual state or past actions. Often appears in set phrases like 平素は格別のお引き立てを賜り…
平素は格別のご高配を賜り、厚く御礼申し上げます。
We would like to express our sincere gratitude for your continued exceptional support.
平素は何かとお世話になり、ありがとうございます。
Thank you for all your help and support as always.
Compound of 平素 (へいそ, 'usual, ordinary') and the topic particle は. The word 平素 itself is a Sino-Japanese term combining 平 (flat, ordinary) and 素 (element, nature).