Expresses a habitual or ongoing state, often with a nuance of 'all along' or 'as always'. Slightly formal; common in written Japanese and polite speech.
He had always thought he should study more.
He never neglects his efforts, as always.
I am always indebted to you for your help.
I've always felt that there are limits to this job.
My mother has always said that health is the most important thing.
日頃 focuses on 'in daily life/normally' as a backdrop for other actions, while 常々 emphasizes a continuously held thought or feeling.
平素 is a very formal, business-letter word for 'usually', while 常々 is somewhat formal but still usable in everyday reflective speech.
常々 emphasizes a habitual or repeated state ('all along, constantly'), while かねて emphasizes that a single plan or fact has existed since an earlier point in time.
常々 means 'habitually, all along' and modifies verbs of attitude or habit, while 日々 more literally marks day-by-day occurrence or passage of time.
Standard kanji spelling; common in news and formal writing.
Kana spelling; used for clarity or in casual writing.
Alternate kanji spelling; less common than 常々.
Reduplication of 常 (つね, 'usual, ordinary'), emphasizing continuity or habitualness. The reading つねづね reflects rendaku (sequential voicing) on the second element.