The correct spelling of the phrase "I am untruthful" is /aɪ æm ʌnˈtruθfəl/. The first sound, /aɪ/, is a diphthong that represents the vowel sounds in "eye". The next sound, /æm/, is pronounced like "am" in "ham". The following sound, /ʌn/, corresponds to the vowel in "bus". The next sound, /ˈtruθfəl/, starts with the consonant cluster /tr/ followed by the vowel sound in "tooth". The word concludes with the syllable pronounced like "ful" in "helpful".
The phrase am untruthful does not have a specific etymology, as it is a combination of two words: am and untruthful.
The verb am is derived from the Old English eom, which means to be (in the first person singular form). It has the same origin as the modern English verb to be.
The word untruthful is derived from the word untruth, which means something that is not true or a falsehood. The suffix -ful is added to untruth to form the adjective untruthful, meaning not telling the truth or being dishonest.
Therefore, the phrase am untruthful simply means I am not telling the truth or I am dishonest.