αὐστηρός has not necessarily an unfavorable meaning. It is well represented by the word austere, it means one who is earnest and severe, strict in his ways, opposed to all levity. By implication it may have the unfavorable meaning of harshness or moroseness. σκληρός has always an unfavorable meaning. It indicates one who is uncivil, intractable, rough and harsh. There is in it the implication of inhumanity.