in essence; at bottom or by one's (or its) very nature
"He is basically dishonest"
"the argument was essentially a technical one"
"for all his bluster he is in essence a shy person"
in an essential manner; in essence
"Essentially, the project failed because we did not have enough funding to launch it properly."
In plain English: Essentially means basically or for all practical purposes, ignoring small details that don't matter much.
"Essentially, we are all just looking for happiness in our daily lives."
Essentially comes from the word essential with the addition of the suffix -ly. It entered English to mean "in an essential manner."