The noun πηχυς (pechus) means forearm, from wrist to elbow. In the classics this word is used to describe the actual arm, but also bent arm-like items such as pieces of weapons and musical instruments. Our word also appears as unit of length, given as one arm's-length, from the elbow to the tip of the middle finger, of a presumably average man.

Our word is from Indo-European extraction and relates to English words like bough and bow. The Hebrew word for arm's-length, or cubit, is אמה ('amma), which relates to אם ('em), meaning mother: she who carries her children "in her bosom" (i.e. against her chest). The Hebrew word for torso is חיק (heq), which comes from a verb that means to embrace or to draw near, which is an activity performed with one's arms.

One's arm terminates in one's hand (χειρ, cheir), which is the body part with which a person exerts their power when they take matters into their hands or lay their hands on someone or give someone a helping hand. The verb αιρεω (haireo) means to grasp, whether by hand or by mind, and describes both physical and mental capabilities. It's this sense of the meaning of our noun πηχυς (pechus) that Jesus refers to when he warns about fretting: nobody can add to one's personal powers, one's social standing or one's intellectual abilities by worrying (the idea that Jesus is talking about adding a full arm's length to one's physical height is of course ludicrous; if that had been his idea, he would have used a proverbially small unit of length, like a jot or hair's width or speck of dust).

Our noun πηχυς (pechus), arm, is used 4 times; see full concordance.