Concise Bible Dictionary:
The word yesterday is used for the previous day (Ex. 5:14; John 4:52; Acts 7:28); and for past time indefinitely, as “a thousand years in Thy sight are but as yesterday;” and as when the Lord Jesus is said to be “the same yesterday, today, and forever” (Psa. 90:4; Heb. 13:8). It is used also as if of “no duration,” as “we are but of yesterday” (Job 8:9). Yesternight is the same as would now be called “last night” (Gen. 19:34; Gen. 31:29,42).
Strong’s Dictionary of Greek Words:
Meaning:
of uncertain derivation; "yesterday"; by extension, in time past or hitherto