na-adjective
inexperienced; incompetent; careless
Often used in humble self-deprecating expressions, especially in formal or polite contexts, to describe one's own lack of skill or experience. Common in set phrases like ふつつか者 (an inexperienced person) or ふつつかながら (although I am inexperienced).
ふつつか者ですが、よろしくお願いします。
I am inexperienced, but I look forward to working with you.
ふつつかな娘ですが、どうぞよろしくお願いいたします。
My daughter is still inexperienced, but please take good care of her.
The origin is uncertain, but it is thought to be a native Japanese word. The kanji 不束 are ateji (当て字) and do not reflect the word's etymology.