The most common and most likely answer to this crossword clue is the 11 letter word HOSPITALITY
I've seen this crossword clue in Independent
H
O
S
P
I
T
A
L
I
T
Y
Buddy explains!

The straight part
We know that "Welcome" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case welcome = hospitality.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 HOSPITALITY mean?
HOSPITALITY noun- The act or service of welcoming, receiving, hosting, or entertaining guests.
- The business of providing catering, lodging and entertainment service; the industry which includes the operation of hotels, restaurants, and similar enterprises.