The most common and most likely answer to this crossword clue is the 7 letter word CURSIVE
I've seen this crossword clue in Financial Times
C
U
R
S
I
V
E
Buddy explains!
The straight part
We know that "joined up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case joined up = cursive.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 CURSIVE mean?
CURSIVE noun- A cursive character, letter or font.
- A manuscript written in cursive characters.
- Joined-up handwriting.
- Running; flowing.
- (of writing) Having successive letters joined together.
- (grammar) Of or relating to a grammatical aspect relating to an action that occurs in a straight line (in space or time).