Banerji is the anglicized version of a Bengali last name (and is becoming increasingly common in India). A person whose last name was বন্দ্যোপাধ্যায় (`praiseworthy teacher') by tradition can choose to use one of a variety of spellings of Bannerjee as an alternate in India without a formal declaration provided it is in good faith.
namitA is the feminine past participle of the Sanskrit verbal root nam, with obvious cognates in other Indo european languages, meaning to bow. (Even though the verb is technically transitive, the participle refers to the subject, not the object.) Since bowing is and was an expression of devotion or respect, the name may be glossed as humble or devoted. It was definitely used as a name in the last generation in a large part of North India.
The -o- comes about because the schwa -a- of Sanskrit developed either into a -o- or -awe- in East Indian languages in positions where it did not disappear. In common words, and in names, an a in the first syllable usually becomes o in Bengali if the next syllable has a front vowel. The ending -a is and was open (as in English car), Bengali vowels are marked by neither length nor stress (rather, stress is a suprasegmental feature). In other Indian languages, the same (technically, merely cognate, though most Indians consider them the `same' name when they are similar in form to the Sanskrit word) name would be pronounced differently.