expression
Used as a noun phrase meaning an additional item or instance. Often followed by a noun or used alone.
もう一つください。
One more, please.
もう一つの問題があります。
There is another problem.
expression, adverb
Adverbial use meaning 'to an even greater degree'. Often used with adjectives or verbs to indicate a higher level than before.
今日は昨日よりもう一つ寒い。
Today is even colder than yesterday.
彼の説明で、問題がもう一つ複雑になった。
His explanation made the problem even more complicated.
expression, adverb
Used in negative contexts to express that something is not quite satisfactory or falls short of expectations. Often appears as もう一つ～ない or もう一つだ.
See also: いまひとつ
この料理はもう一つ味が足りない。
This dish is not quite flavorful enough.
彼の提案はもう一つだ。
His proposal is lacking something.