I want to know is there a dictionary available for browsers which shows the meaning of word if i long press on word like I do in moon reader.

[ill420smoker]

These apps both show definitions after highlighting a word and selecting the 'copy' option:

News Dictionary-WordSnitch (online only, copy method & widget method)
https://play.google.com/store/apps/details?id=com.yaki.wordsplash

Babylon Translator (online/offline, multiple languages)
https://play.google.com/store/apps/details?id=com.babylon.translator
viewtopic.php?f=430&t=1226189&hilit=Babylon

Hope that helps