[adjective], [adverb] [not gradable]My earliest (= first) memory is of being held up as a baby to watch Neil Armstrong landing on the moon on TV.I'm very busy, so I won't be with you till 4 o'clock at the earliest (= not before 4 o'clock, and probably after it).
EARLIEST
Meaning of EARLIEST in English
Cambridge English vocab. Кембриджский английский словарь. 2012