The most common and most likely answer to this crossword clue is the 7 letter word ENLISTS
I've seen this crossword clue in The Daily Telegraph
E
N
L
I
S
T
S
More clues leading to the result ENLISTS
- Heel finally heals after nurse gets involved
- Priest, gathering town's last holy men, joins service
- Silent, antagonistic son joins army
- Alarmingly silent son becomes soldier
- Silent revolutionary holding small signs up
- Nitless new recruits
- Joins up broken lines thus vacantly
- Recruits surprisingly listen on square
- Comes into force?
- Enters tinsel to become leading star
Buddy explains!

The straight part
We know that "Comes into force" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case comes into force = enlists.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 ENLISTS mean?
ENLISTS noun- One who is enlisted, usually in a military service.
- To enter on a list; to enroll; to register.
- To join a cause or organization, especially military service.
- To recruit the aid or membership of others.
- To secure; to obtain.