The most common and most likely answer to this crossword clue is the 7 letter word LACKING
I've seen this crossword clue in The Times
L
A
C
K
I
N
G
More clues leading to the result LACKING
- Working lazily, not beginning to be inadequate
- Not doing enough work missing son is absent
- Polish bishop’s left short
- A sort of gloss ruler is missing
- Needing support, Bolshevik leader turns to Left
- Lazy son’s gone missing
- Inadequate society quits idling
- In need of sleep, for starters, for relaxing
- Protection for the ruler's not there
- Luxembourg bigwig has a cold, is unavailable
Buddy explains!

The straight part
We know that "missing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case missing = lacking.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 LACKING mean?
LACKING verb- To be without, to need, to require.
- To be short (of or for something).
- To be in want.
- To see the deficiency in (someone or something); to find fault with, to malign, reproach.
- The absence of something; a lack.
- Missing or not having enough of (a good quality, etc).
- Not carrying a firearm.