preposition
in the time after (a specified time or event in the past) :from (a point in the past) until the present time
since the year one
since when?
used to show that you are surprised and often angry, annoyed, or doubtful about what someone has said or done
conjunction
in the period after the time when
from the time in the past when
used to introduce a statement that explains the reason for another statement
adverb
from a past time until now
after a time in the past
before the present time
US