The most common and most likely answer to this crossword clue is the 9 letter word COLONNADE
I've seen this crossword clue in Independent
C
O
L
O
N
N
A
D
E
More clues leading to the result COLONNADE
- Building feature: walls in Nevada and Delaware
- Columns needing punctuation and edited English
- A London vagrant sheltering in church portico
- Peristyle showing sign of listing disturbed Dean
- Reconstruct ace London architectural feature
- Architectural row: a media centre in North-East
- Mark Dean fashioned in a range of columns
- Row of trees in area in London somehow protected by church
Buddy explains!

The straight part
We know that "portico" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case portico = colonnade.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 COLONNADE mean?
COLONNADE noun- A series of columns at regular intervals.
- A peristyle.
- A portico or stoa.
- A regular row of anything, such as trees.