bubble under

US /ˈbʌb.əl ˈʌn.dər/
UK /ˈbʌb.əl ˈʌn.dər/
"bubble under" picture
1.

to be almost successful or popular but not quite there yet

:
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The band has been bubbling under for years, but they haven't had a hit song yet.
•
Her new book is bubbling under, and many critics expect it to be a bestseller soon.
:
on the verge of successon the cusp of popularityemergingup-and-comingpotential hit
:
bubble under the radarbubblebubblybubble bathbubble gumbubble and squeakbubble tea