The most common and most likely answer to this crossword clue is the 8 plus 7 letter word ELECTRIC CURRENT
E
L
E
C
T
R
I
C
C
U
R
R
E
N
T
Buddy explains!
The straight part
We know that "“I”" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case “i” = electric current.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.