N1
ただ〜のみ
Nothing but, Only, All that remains is, There is nothing left but to
私たちにはもう何もできない。ただ医者を信じて待つのみだ。
There is nothing more we can do. All we can do is trust the doctor and wait.
Explanation
「ただNのみ」 means 'nothing but N' or 'all that is left is N'. At a critical moment every other way is gone, and only this one path or fact remains. The sentence usually ends in 「〜のみだ」 or 「〜のみである」: 「人事を尽くした。今はただ吉報を待つのみである」 (We have done all we can. Now we can only wait for good news), 「残された道は、ただ前進あるのみだ」 (The only way left is forward). It is classical written language, solemn and resolute, found in pledges, sayings, reports and essays. Common with 「あるのみ」, 「待つのみ」, 「信じるのみ」, 「願うのみ」.
Mixed up with
「ただ〜のみ（だ）」: old-style written language, solemn; the only way out when facing a great test.
「ただ〜だけ（だ）」: modern and general; neutrally limits an amount or range.
「ただ〜ばかり（だ）」: often a negative, 'doing nothing but' tone, e.g. 「ただ祈るばかりで何もしない」 (just prays and does nothing).