o'clock
Longman Dictionary of Contemporary English 5++LDOCE 5++o'clock /əˈklɒk $ əˈklɑːk/ ●●● S1 W3 adverb one o'clock/two o'clock etc TMCone of the times when the clock shows the exact hour as a number from 1 to 12 1点钟/2点钟等 It’s already 9 o'clock. 已经9点钟了。 The meeting is at 10 o'clock. 开会时间是10点钟。 ► Do not use o'clock when mentioning minutes or parts of an hour: ten past nine (NOT ten past nine o'clock) | half past one (NOT half past one o'clock). Do not use o'clock when writing the time in the form 1.00,2.00 etc.不要用 o'clock 表达分钟或非整点时间: ten past nine (不说 half past nine o'clock) 9点10分 | half past one (不说 half past one o'clock) 1点半. 把时间写成1.00,2.00等形式时，不要用 o'clock.
Examples from the Corpus
o'clock• It's 5 o'clock.• It's exactly 10 o'clock.Origin o'clock (1400-1500) of the clocko'clock adverbChinese
when the the of clock Corpus one times
o'clock
o'clock S1 W3 /əˈklɒk $ əˈklɑːk/
adverb
It’s already 9 o'clock.
The meeting is at 10 o'clock.
► Do not use o'clock when mentioning minutes or parts of an hour: ten past nine (NOT ten past nine o'clock) | half past one (NOT half past one o'clock). Do not use o'clock when writing the time in the form 1.00, 2.00 etc.
o'clock S1 W3 /əˈklɒk $ əˈklɑːk/
adverb Date: 1400-1500
Origin: of the clock
one o'clock/two o'clock etc one of the times when the clock shows the exact hour as a number from 1 to 12:Origin: of the clock
► Do not use o'clock when mentioning minutes or parts of an hour: ten past nine (NOT ten past nine o'clock) | half past one (NOT half past one o'clock). Do not use o'clock when writing the time in the form 1.00, 2.00 etc.