An Etymological Dictionary of the German Language/sicher
sicher, adj., ‘sure, certain, trusty,’ from MidHG. sicher, OHG. sihhū̆r, ‘careless, unconcerned; sure, protected, confident’; to these are allied OSax. and AS. sicor, ‘free from guilt and punishment,’ MidE. sîker, Du. zeker (OHG. sihhorô(illegible text), ‘to justify, protect, promise, vow,’ OSax. sicorôn, ‘to set free’). It is based on the common West Teut. loan-word Lat. sêcûrus (phonetic intermediate form sĕcûrus, the accent of which was Germanised when the word was borrowed); comp. Ital. sicuro, Fr. sûr. The term was naturalised in G. before the 7th cent., as is shown by the permutation of k to ch. Was it first introduced through the medium of legal phraseology? Comp. OHG. sihhorôn, ‘to justify, purgare.’