This is the 210th most frequent French word.
tard
Late.
In this sentence, 'tard' is used as an adjective to indicate 'late' in terms of time.
Il est déjà tard.
It is already late.
'Tard' is used here in a set expression, paired with 'tôt' (early), to indicate a time-related inevitability or eventuality.
Tard ou tôt, il faudra y penser.
Sooner or later, we will have to think about it.
Here, 'tard' functions as an adverb to describe the timing of the action of arriving.