The most common and most likely answer to this crossword clue is the 14 letter word COUNTERCULTURE
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The straight part
We know that "bohemianism" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bohemianism = counterculture.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COUNTERCULTURE mean?
COUNTERCULTURE noun- Any culture whose values and lifestyles are opposed to those of the established mainstream culture, especially to western culture.