noun
first time; first occurrence
Refers to the first instance of an event or series. Often used in contexts like 'the first meeting', 'the first edition', or 'the first round'.
第一回の会議は来週の月曜日です。
The first meeting is next Monday.
noun which may take the genitive case particle 'no'
Used attributively with の to modify a noun, indicating the first in a series or sequence.
これは第一回の試みです。
This is the first attempt.
最初 is a general word for 'first' or 'beginning', while 第一回 specifically refers to the first occurrence in a numbered sequence.
Compound of 第一 (first) and 回 (time, occurrence). The reading だいいっかい results from a euphonic change where いち (one) becomes いっ before かい.