1.
If someone, usually a thief, breaks in, they get into a building by force.
Masked robbers broke in and made off with $8,000...
PHRASAL VERB: V P
see also break-in
2.
If you ~ on someone’s conversation or activity, you interrupt them.
O’Leary broke in on his thoughts...
Mrs Southern listened keenly, occasionally breaking in with pertinent questions...
‘She told you to stay here,’ Mike broke in.
= butt in
PHRASAL VERB: V P on n, V P, V P with quote
3.
If you break someone in, you get them used to a new job or situation.
The band are breaking in a new backing vocalist.
PHRASAL VERB: V P n (not pron), also V n P
4.
If you ~ something new, you gradually use or wear it for longer and longer periods until it is ready to be used or worn all the time.
When breaking in an engine, you probably should refrain from high speed for the first thousand miles...
PHRASAL VERB: V P n (not pron), also V n P