Without experience (apeiros). Old adjective (alpha privative and peira, trial). Inexperienced. The babe (nēpios, old word, negative nē and epos, word like Latin infans, infant, not able to talk), not able to chew if one uses only milk and is without teeth. Perhaps moral truth is meant by “word of righteousness” (cf. Heb 1:2; Heb 2:3 for the word spoken by Christ).