The most common and most likely answer to this crossword clue is the 9 letter word INFANTILE
I've seen this crossword clue in The Times
I
N
F
A
N
T
I
L
E
More clues leading to the result INFANTILE
- Child’s cooler if wearing fashionable hat
- Popular headgear for supporter, perhaps, is not entirely sensible
- Like children lined up around worker?
- Trendy cool hat is childish
- Home supporter with headwear is childish
- Very silly wearing hat to keep cool
- Wearing cooler hat, not so sophisticated
- Having fashionable fake tan in portfolio is not grown up or clever
- Marching as a column, stopped by soldier maybe at an early stage
- Immature female opposed to standing in assembled line
Buddy explains!
The straight part
We know that "not entirely sensible" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not entirely sensible = infantile.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 INFANTILE mean?
INFANTILE adjective- Pertaining to infants.
- Childish; immature.