From BiblePortal Wikipedia

Vine's Expository Dictionary of NT Words [1]

1: Αὐστηρός (Strong'S #840 — Adjective — austeros — ow-stay-ros' )

akin to auo, "to dry up" (Eng., "austere"), primarily denotes "stringent to the taste," like new wine not matured by age, unripe fruit, etc; hence, "harsh, severe,"  Luke 19:21,22 .

 Luke 19  Matthew 25:24 John 6:60 Acts 9:5 26:14 James 3:4  Jude 1:15FierceHard.

Webster's Dictionary [2]

(1): Sour and astringent; rough to the state; having acerbity; as, an austere crab apple; austere wine.

(2): Severe in modes of judging, or living, or acting; rigid; rigorous; stern; as, an austere man, look, life.

(3): Unadorned; unembellished; severely simple.

King James Dictionary [3]

AUSTE'RE, a. L. Austerus.

1. Severe harsh rigid stern applied to persons as an austere master an austere look. 2. Sour harsh rough to the taste applied to things as austere fruit, or wine.

International Standard Bible Encyclopedia [4]

ôs - tēr ´ αὐστηρός , austērós , "harsh," "rough"): Twice used by Christ in the parable of the Pounds ( Luke 19:21 ,  Luke 19:22 ), and of special significance as illustrating the false conception of God cherished by the sinful and disobedient. The fear resident in a guilty conscience sees only sternness and severity in God's perfect righteousness. The word may be made an eminent study in the psychology of an evil heart. Wrongdoing eclipses the soul's vision of God's love and pictures His righteousness as harsh, unfeeling, partial, unjust, forbidding. The awfulness of sin may Thus be seen in its power so to pervert the soul as to make goodness seem evil, justice unjust, and even love unlovely. Compare "hard" σκληρός , sklērós , "dried up," "harsh") in the parable of the Talents ( Matthew 25:24 ).