Wikipedia points out:  The use of a single word or cognate for "inch" and "thumb" is common in many other  Indo-European languages , for example,  French :  pouce  inch/thumb;  Italian :  pollice  inch/thumb;  Spanish :  pulgada  inch,  pulgar  thumb; Portuguese :  polegada  inch,  polegar  thumb;  Swedish :  tum  inch,  tumme  thumb;