beginning; early part
Used for the early part of a century, year, period, or era. Often follows a time expression (e.g., 20世紀初頭, 令和初頭).
Many inventions were born at the beginning of the 20th century.
Japan's economy was unstable in the early Reiwa period.
Many inventions were made in the early 20th century.
Society changed dramatically from the early to the late 20th century.
末 means the 'end' or 'latter part' of a period, directly contrasting with 初頭's 'early part', as in 20世紀初頭 vs 20世紀末.
初等 (same pronunciation) means 'elementary' as in 初等教育 (elementary education), while 初頭 refers to the early part of a time period like a century or era.
primacy effect
Compound of 初 (しょ, 'first') and 頭 (とう, 'head' or 'beginning'). The reading しょとう is standard Sino-Japanese.