Is は a particle in こんにちは and こんばんは?


Is は a particle in こんにちは and こんばんは?




Yes. This は is the same as the topic marker は.

These expressions were originally the start of a greeting, as in,
[今日]{こんにち}はお[元気]{げんき}でしょうか ("You're feeling well today?") or [今晩]{こんばん}はいかがですか
("How are you this evening?"), etc. Over time, through regular and frequent
use, the opening portions came to be used independently as simplified
greetings.

According to Shogakukan's [国語]{こくご}[大]{だい}[辞典]{じてん} entry for [今日]{こんにち}は:

> （「今日は…」と続けた挨拶語の下略されたもの）  
>  (omitting the portion of the greeting continuing on after " _konnichi
> wa_...")

