What's the right spelling of (something I hear, but cannot find, as) "часно слово"?

Question

I often hear in Russian an expression that I suppose can be translated as "I swear it", or "I give you my word". I hear something as "часно слово", "час на слово" ?

What is its right spelling and what does it exactly mean?

Remark: I cannot find it in lingvo, wikipedia, gramota nor by translation, even trying with combinations of possible spelling mistakes (exchanging ч by ш, the о's by a's, итд.)

Edit: of course, my ear can just be unmature to hear Russian and detect all possible spellings .

Answer 1

It is actually [моё] честное слово, which can be translated as an honest word [of mine]. Phrase давать честное слово is interchangeable with обещать (to promise).

There is also a word клясться, but this is more close to to vow: it is somewhat stronger than making a promise.