The most common and most likely answer to this crossword clue is the 7 letter word IDEALLY
I
D
E
A
L
L
Y
More clues leading to the result IDEALLY
- English friend the writer would put first, in theory
- I trade extremely lucratively — in theory
- Fish is given to friend in a perfect world
- In a perfect world I trade with empty lorry
- Kiddies regularly team up, in theory
- In a perfect world, I would start to embrace mate
- I should note friend with a perfect manner
- In the best case, island truly needs to replace leader with daughter
- In a perfect world, I had European associate
- Idiots initially loiter without point in a perfect world
Buddy explains!

The straight part
We know that "in theory" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in theory = ideally.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 IDEALLY mean?
IDEALLY adverb- In an ideal way; perfectly.
- Given ideal circumstances; preferably.