in a close relation or position in time or space
"the onsets were closely timed"
"houses set closely together"
"was closely involved in monitoring daily progress"
in a close manner
"the two phenomena are intimately connected"
"the person most nearly concerned"
In a close manner.
"She watched him closely as he opened his wallet to count the cash."
In plain English: Closely means being very near to someone or something, either physically or by paying great attention to details.
"The friends sat closely together on the bench to keep warm."
Usage: Use closely to describe doing something with great attention to detail or in immediate proximity to someone or something. Avoid confusing it with "close," which functions as an adjective describing nearness rather than the manner of an action.
The word closely is formed by adding the suffix -ly to the adjective close. This construction simply turns the idea of being near into an adverb describing how an action is performed.