The word "offenceless" is spelled with two F's, despite the fact that it may seem more intuitive to spell it with only one. This is because the word is derived from the Old French word "ofenseles," which itself has two F's. The IPA phonetic transcription for "offenceless" is /əˈfɛns.ləs/. It is pronounced with primary stress on the second syllable and a secondary stress on the first syllable.
Free from a disposition to offend.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.
The word offenceless is derived from the root word offense, which comes from the Latin word offendere. Offendere means to strike against, stumble, or to displease. The suffix -less is added to the word offense to create offenceless, meaning without offense or incapable of causing offense.