The etymology of this word remains problematic, and the FEW’s proposed association with prothyrum (‘einfriedigung vor der tür’, i.e. ‘grill or fence in front of a door’) and its cognate expression faire le prorne (i.e. ‘to boast’), attested only once in a thirteenth-century Picard text, is certainly not the complete answer (cf. Baldinger, Etymologien iii 291-92).