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第3月曜日 I'm not sure the actual meaning.

  1. 3rd Monday that some month may not have this day ( Monday that the date is the third ) for clearer explainantion in picture below

[![enter image description
here](https://i.stack.imgur.com/Zikyc.png)](https://i.stack.imgur.com/Zikyc.png)

  2. Monday that is in the third week ( 1 month has 4 weeks and this 第３月曜日 is Monday that's in 3rd week )
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2020-05-15T10:32:11.127
77311
2020-05-16T01:19:01.577
38446
question
meaning context
第3月曜日 3rd Monday or Monday in the third week
第3月曜日 refers to the Monday that comes for the third time in the given month.
All months have 第3月曜日 because all months have at least 21 days. Likewise,
there is no month that has 第6月曜日. Note that 第3 in Japanese never refers to the
third day of a month in the first place.

Also note that your definition #2, "Monday that is in the third week", is
probably inaccurate. For example, The 第3月曜日 of September 2020 is the 21th (see
the calendar below), but I think many people think "Monday that is in the
third week" refers to the 14th.

[![enter image description
here](https://i.stack.imgur.com/GNbyym.png)](https://i.stack.imgur.com/GNbyym.png)
CC BY-SA 4.0
2020-05-16T01:19:01.577
77336
2020-05-16T01:19:01.577
5010
77311
answer