The most common and most likely answer to this crossword clue is the 10 letter word EUPHEMISMS
I've seen this crossword clue in Financial Times
E
U
P
H
E
M
I
S
M
S
Buddy explains!

The straight part
We know that "Inoffensive substitute words" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case inoffensive substitute words = euphemisms.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 EUPHEMISMS mean?
EUPHEMISMS noun- The use of a word or phrase to replace another with one that is considered less offensive, blunt or vulgar than the word or phrase which it replaces.
- A word or phrase that is used to replace another in this way.