This adjective describes someone without experience or skill in a particular area. Classical Greek used it for the untrained, the inexperienced, or those unfamiliar with specific practices. Hebrews 5:13 employs it to describe believers still on a milk diet: they are 'unskilled in the word of righteousness.' Like infants who haven't learned to eat solid food, these believers haven't developed the capacity to digest deeper theological truth. The term emphasizes lack of practical experience and developed skill, not mere theoretical ignorance.